Tourette syndrome (TS), named after the French neurologist who first described it, is a neurological disorder characterized by motor tics (brief, non-rhythmic, stereotyped movements) and vocal tics.

TS is usually first noticed in childhood between 2 and 15 years of age, although there have been cases of delayed onset (starting around 21 years of age). Depending on how strictly it's defined, experts estimate that TS affects 1 in 100 people. Boys are 4 times more likely to be diagnosed with this condition than girls.

Although there is no cure for TS, most people do not need medical treatment if symptoms aren't bothersome. Severe cases of TS can cause behaviour that many people find bizarre, rude, or alarming. Many people who have heard of this condition associate it with loud and uncontrollable swearing. This is one possible symptom of TS, but it's a fairly rare one. Most people with TS have much less severe tics.

People with TS may also have other associated behaviours or symptoms, such as attention deficit hyperactivity disorder (ADHD) or obsessive-compulsive disorder (OCD). About half of the people who have TS also have OCD or ADHD. Women are more likely to have OCD together with TS, and men are more likely to have ADHD together with TS. ADHD tends to appear 2 to 3 years before TS, but OCD tends to appear 5 to 6 years after a diagnosis of TS. Not everyone with TS has these conditions and the link between TS and these conditions is unclear.

The severity of tics often diminishes with age and resolves by age 18 for about half of the people with this condition. Though symptoms of TS usually improve during late teenage years, other medical conditions associated with TS, such as depression and anxiety, may continue into adulthood. People with TS have a normal life expectancy and intelligence.

Although the exact cause of TS is unknown, researchers believe that is it likely caused by changes in certain areas of the brain as well as imbalances of the chemical messengers in the brain (such as dopamine, serotonin, and norepinephrine).

Genetics and family history also play a role. TS was once thought to be genetically inherited as a dominant trait, but recent studies show that the genetics of TS is much more complicated. In most cases, TS is inherited from both parents.

Children of parents with TS may not develop TS at all or may develop TS with varying degrees of severity. And some people who have TS have no family history of the condition. Boys born to a parent with TS are more likely than girls to have the condition. Girls, however, are more likely to have associated behaviour conditions such as OCD.

Environmental factors may also play an important role in the development of TS.

The symptoms of TS usually appear before the age of 18. If they develop afterwards, TS is unlikely to be diagnosed because the symptoms are usually less severe or are attributed to other medical conditions. Symptoms are often worse before the mid-teens and improve as the person gets older. But for about 10% of people with TS, the symptoms get progressively worse into adulthood.

Most people with TS have simple motor and vocal tics. Continual eye blinking is one of the most common simple motor tics. Others include grimacing, head jerking, shrugging, and leg tapping. Simple vocalizations can include constant throat clearing, sniffing, grunting, barking, or other noises.

Some people with TS experience more complex motor and vocal tics that involve more muscles and more complicated movements. Complicated motor tics include shrugging combined with head jerking, copying other people's movements (echopraxia), sniffing objects, touching other people, and, very rarely, self-harming behaviours such as banging the head or biting the lip.

Complex vocal tics can involve words and groups of words, including repeating other people's words (echolalia) and loud swearing and cursing (coprolalia).

Coprolalia is a symptom popularly associated with TS, but only a minority of people have this symptom. Many people with TS can control their symptoms for a few minutes to hours at a time, but it's like trying to hold back a sneeze. It must eventually come out, and it's likely to come out in a bigger way if it's delayed.

People with TS often find that their symptoms get worse when they're nervous and ease when they're relaxed or concentrating hard on something.

People with TS may also have other conditions that affect their behaviour. Obsessive-compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD) are very common in people with TS. These additional conditions may cause more functional and social problems for people with TS than the tics caused by TS.

ADHD is characterized by poor attention span and impulsive behaviours, whereas OCD involves repetitive and intrusive thoughts or repetitive behaviours. In adults, this often involves habits like continually checking that the door is locked, making sure the oven is turned off, or endless hand washing. A typical OCD behaviour in children is touching something with one hand, then feeling like they must "even things out" by touching it with the other hand.

People with TS may also be more at risk of experiencing depression and anxiety.

Tourette syndrome (TS) is diagnosed based on symptoms – a person must have both multiple motor tics and one or more vocal tics for at least one year, before the age of 18 (or in some delayed cases, 21 years), to be diagnosed with TS. The motor and vocal tics, however, do not have to occur continuously or at the same time.

Doctors may order magnetic resonance imaging scans (MRIs), computerized axial tomography (CAT) scans, or blood tests, but their purpose is to rule out other neurological problems - not to find TS.

Most physicians can easily diagnose people with typical TS symptoms. However, people with atypical symptoms or symptoms that start later in life may be more difficult to diagnose. It may take a while before a person gets a diagnosis of TS, mainly because many mild tics may be attributed to other causes (e.g., constant sniffing due to allergies).