Data on epilepsy in pervasive developmental disorder not otherwise specified are few and scanty. Seventy-seven patients with pervasive developmental disorder not otherwise specified were compared with 77 with autistic disorder, matched for age and sex. The 2 groups were divided into 3 subgroups each: A, without electroencephalography (EEG) paroxysmal abnormalities or epilepsy; B, with EEG paroxysmal abnormalities without epilepsy; and C, with epilepsy. Mild mental retardation (P < .01), pathological neurological examination (P < .05), cerebral lesions (P < .01), abnormal EEG background activity (P < .001), and associated genetic pathologies (P < .01) were more common in pervasive developmental disorder not otherwise specified. Familial antecedents for epilepsy prevailed in subgroup C (P < .01). Epilepsy occurred in 35.1% of patients with pervasive developmental disorder not otherwise specified, with no statistically significant difference compared with autistic disorder. The mean age of seizure onset was earlier (2 years 8 months) in pervasive developmental disorder not otherwise specified (P < .000). Seizure outcome was better in autistic disorder. Genetic diseases and cerebral lesions should be investigated in pervasive developmental disorder not otherwise specified to clarify the etiological and clinical features.