A link has been postulated between regressive autism and the spectrum of epileptic encephalopathic conditions including Landau-Kleffner syndrome with the suggestion that subclinical epilepsy may be causative of regression in autism. This is an audit of investigation using sleep electroencephalograms (EEG) in 64 children (56 males, 8 females; mean age 35.6mo [SD 8.2mo]; range 18–48mo) with autism. No child had a history suggestive of epilepsy. Thirty-nine of the children presented with regressive autism and 20 of the participants showed some epileptiform abnormality. There was no significant difference in epileptiform activities in those who showed regression compared with those who did not. No child showed electrical status epilepticus with continuous spike-wave discharges in slow sleep. There was no evidence that these cases of autism with and without regression were associated with epileptic encephalopathy. The significance of epileptiform discharges without epilepsy in the sleep EEG in autism remains unknown.