Correlations between occurrence of complex partial seizures and altered sleep duration were analyzed in a small but strongly homogeneous population of temporal lobe epilepsy patients. Sleep deprivation and oversleep were determined individually; 682 epileptic seizures occurring on 4,995 days were related to occasional alterations of night sleep duration. The seizure-inducing effect of an actual relative sleep deprivation was 67-100% in four cases and 49-64% in four cases. Oversleep had no consistent seizure-provoking effect. Relative sleep deprivation may have a seizure-provoking effect, especially in temporal lobe epilepsy. This information may be used to instruct epileptic patients concerning sleep hygiene which might improve the efficacy of antiepileptic drug (AED) treatment, even if no change is made in medication.