In order to evaluate the effects on behaviour of some anti-epileptic drugs, we studied 300 children treated with phenobarbital and other drugs; their age ranged from 3.1 months to 15.9 years. The children were divided into two groups: group A: 197 (116 male and 81 female) children, mean age +/- SD 5.3 +/- 2.8 years, treated with phenobarbital; group B: 103 (66 male and 37 female) children, mean age 6.4 +/- 3.1 years, treated with anti-epileptic drugs other than phenobarbital. In all patients hyperactivity, irritability, disturbances of sleep, and drowsiness were investigated. The parents of patients completed a questionnaire with seven items. In group A, 150 (76.1%) children showed one or more behaviour disturbances, while in Group B a smaller number of patients 32 (31%) had such disorders. There was a significant difference between the two groups (P < 0.0001). The most frequent disorder was hyperactivity. The results of this study suggest that anti-epileptic drugs, in particular phenobarbital, can cause behaviour disturbances.