Generally, TS is diagnosed by obtaining a description of the tics and evaluating family history. For a diagnosis of TS to be made, both motor and phonic tics must be present for at least 1 year. Neuroimaging studies, such as magnetic resonance imaging (MRI), computerized tomography (CT), and electroencephalogram (EEG) scans, or certain blood tests may be used to rule out other conditions that might be confused with TS. However, TS is a clinical diagnosis. There are no blood tests or other laboratory tests that definitively diagnose the disorder.

Studies show that correct diagnosis of TS is frequently delayed after the start of symptoms because many physicians may not be familiar with the disorder. The behavioral symptoms and tics are easily misinterpreted, often causing children with TS to be misunderstood at school, at home, and even in the doctor's office. Parents, relatives, and peers who are unfamiliar with the disorder may incorrectly attribute the tics and other symptoms to psychological problems, thereby increasing the social isolation of those with the disorder. And because tics can wax and wane in severity and can also be suppressed, they are often absent during doctor visits, which further complicates making a diagnosis.

In many cases, parents, relatives, friends, or even the patients themselves become aware of the disorder based on information they have heard or read in the popular media.