The largest cluster of E200K familial Creutzfeldt-Jakob disease (fCJD) which occurs is in Jews of Libyan origin in Israel. Insomnia is a very common early complaint in those patients and may even be the presenting symptom. The aim of this study was to assess and characterize sleep pathology in E200K fCJD patients. To do so, sleep studies of 10 consecutive fCJD patients were compared with those of 39 age and gender-matched controls. All patients presented pathological sleep characterized by fragmentation of sleep, loss of sleep spindles and reduced REM sleep amount. Respiration was characterized by irregular rhythm, periodic breathing, apneas and hypopneas, either central or obstructive. EMG recordings revealed repeated movements in sleep, with loss of REM atonia. Comparing to controls, a significant decrease of total sleep time, sleep efficacy and slow-wave sleep as well as a significant increase in the number of awakenings, apnea-hypopnea index and mixed and central apneas were evident in CJD patients. Comparison of two sequential sleep studies in one patient revealed a 40 % reduction of the total sleep time, a 40 % reduction in sleep efficacy and a 40-fold increase of the number of arousals in the second study. A significant correlation was found between the disease severity, as reflected by the CJD Neurological Scale and Periodic leg movement index. These definite and characteristic sleep pathologies in patients with fCJD associated with the E200K mutation may serve as a new diagnostic tool in the disease.