At a childpsychiatric outpatient department 96 children ages 2-16 years were treated with clonidine 4 μg/kg/day. These children were diagnosed (DSM-III-R) as Tourette Syndrome (n = 54, 11 non-hyperactive and 43 hyperactive), Attention Deficit Hyperactivity Disorder (n = 26) and as (hyperactive) Pervasive Developmental Disorder (n = 16). After at least three months of open treatment with clonidine a clinically significant improvement was seen in 45% of the non-hyperactive Tourette patients, 72% of the hyperactive Tourette patients, 65% of the ADHD patients, and 63% of the hyperactive PDD children. The major side effect was sleepiness, which occured in 64% of the children in the first month. Five weeks after dosage was installed 21% of the patients still complained of side effects.