Fastening an electroencephalography (EEG) electrode to the forehead with a disposable self-adhesive electrode in ambulatory polysomnographic recordings is a tempting option. The aim of the present study was to clarify, whether the sleep parameters change if sleep stage scoring is based on the frontopolar EEG derivation instead of the commonly used central EEG derivation. Ten healthy subjects and ten patients with sleep disorders were studied. The scoring agreements between the two EEG derivations were close to previously observed inter-scorer agreements. In addition, it was found that using frontopolar scoring would not have caused any changes in the clinical diagnosis of the patients as compared to the standard scoring method. Interestingly, higher percentage of slow wave sleep and a lower amount of sleep stage 2, as expected, was obtained by frontopolar scoring in healthy subjects but such difference was not found in frontopolar scoring of the patients. This might implicate a deficit in the synchronization producing mechanisms in the frontal cortex of the patients. In ambulatory studies with a limited number of channels frontopolar EEG recording could be used as a single electrode because of its simplicity and probable sensitivity to changes in nocturnal brain activity. (