Nocturnal EEG, electro-oculograms, and electromyograms were studied in nine patients with dystonia musculorum deformans and in nine healthy controls. Electrodes were placed over frontal, central, and occipital regions in accordance with the international 10-20 system of electrode placement. A standard bipolar montage was used for the recordings, and records were scored independently in accordance with the manual of Rechtschaffen and Kales. All patients were found to sleep poorly. Patients in advanced stages of dystonia all displayed an EEG pattern characterized by pronounced, high-amplitude (greater than 150 microV) spindles that were continuous for all stage 2 and portions of stage 3 sleep. Other sleep parameters were also disturbed. Sleep spindles become less frequent and diminish in amplitude with advancing age. The spindle activity of patients with advanced dystonia presents a stark contrast to this pattern and may underscore their clinical significance.