The frequency of tics in a 10-year-old boy suffering from Gilles de la Tourette syndrome was investigated in the laboratory and at home using counts of tics made by the parents. The study spanned 20 months during which time the patient was treated with haloperidol. Parents' counts were reliable and valid. Stressful life events overcame positive medication effects, and symptom level varied markedly with the activities in which the child engaged. Such situational variability may explain the previously reported waxing and waning of symptoms. Findings also suggested that specific counseling be given when haloperidol is prescribed in order to prepare parents and patients for any apparent worsening of the disorder that may actually be due to the presence of stressful life events.