Sleep has been shown to be important to memory. Both sleep and memory have been found to be abnormal in patients with epilepsy. In this study, we explored the effects that nocturnal epileptiform discharges and the presence of a hippocampal lesion have on sleep patterns and memory. Twenty-five patients with focal epilepsy who underwent a 24-hr ambulatory EEG also completed the Everyday Memory Questionnaire (EMQ). The EEG record was scored for length of time spent in the various sleep stages, time spent awake after sleep onset, and rapid eye movement (REM) latency. Of these sleep variables, only REM latency differed when the epilepsy patients were divided on the bases of either presence/absence of nocturnal discharges or presence/absence of a hippocampal lesion. In both cases, presence of the abnormality was associated with longer latency. Furthermore, longer REM latency was found to be a better predictor of EMQ score than either number of discharges or presence of a hippocampal lesion. Longer REM latency was associated with a smaller percentage of time spent in slow-wave sleep in the early part of the night and may serve as a particularly sensitive marker to disturbances in sleep architecture.