With the increasing interest in callosotomy as treatment for intractable epilepsy, it seems to be important to define the neuropsychological consequences of the related surgical operation. 8 patients suffering from drug-resistant seizures underwent section of the corpus callosum, 6 in the anterior part only and 2 undergoing complete two-stage commissurotomy including the posterior part. Before the callosotomy the patients were studied using a cognitive, affective and behavioural battery which was repeated 15 and 90-100 days after the operation. The patients with sufficient I.Q. were described in more detail using the cognitive parameters; the social and motor behaviour of Lennox-Gastaut subjects are accurately reported. No disconnection syndrome was ever observed after the partial commissurotomy while it occurred in one of the two complete callosotomies. The patients showed longer reaction times and a mild impairment of linguistic, praxic, memory and motor functions in the former evaluation (15 days), but there was consistent improvement in the latter check up. At the 90-100 day follow-up the Lennox-Gastaut patients responded more readily to the environmental stimulations and their postural, motor and behavioural functions were unchanged or improved, with respect to presurgical performances. The social and emotional behaviour of all the patients had always improved by the time the long-term evaluation (90 days) was performed. Finally, by limiting the callosotomy to the anterior part only, the neurological and psychological consequences seem to be limited.(ABSTRACT TRUNCATED AT 250 WORDS)