We previously reported that IQ was significantly lowered in a group of toddler-aged children randomly assigned to receive phenobarbital or placebo for febrile seizures and there was no difference in the febrile seizure recurrence rate. We retested these children 3-5 years later, after they had entered school, to determine whether those effects persisted over the longer term and whether later school performance might be affected. On follow-up testing of 139 (of the original n = 217) Western Washington children who had experienced febrile seizures, we found that the phenobarbital group scored significantly lower than the placebo group on the Wide Range Achievement Test (WRAT-R) reading achievement standard score (87.6 vs 95.6; p = 0.007). There was a nonsignificant mean difference of 3.71 IQ points on the Stanford-Binet, with the phenobarbital-treated group scoring lower (102.2 vs 105.7; p = 0.09). There were five children in our sample with afebrile seizures during the 5-year period after the end of the medication trial. Two had been assigned to phenobarbital, and three had been in the placebo group. We conclude there may be a long-term adverse cognitive effect of phenobarbital on the developmental skills (language/verbal) being acquired during the period of treatment and no beneficial effect on the rate of febrile seizure recurrences or later nonfebrile seizures.