The effects of 20 mg zolipidem were studied in an open, polysomnographically-monitored 179 day trial in 14 elderly psychiatric patients suffering from severe insomnia. After a placebo run-in of 7 days, zolpidem was given for 179 days followed by a 30-day wash-out period. Polysomnographic recordings (PSG) were performed just before active treatment; 30, 90 and 179 days into the treatment period; and at the end of the wash-out period. Statistically significant improvements in total sleep time, sleep efficiency and percentage of rapid eye movement sleep were observed after 30 days, all of which were maintained at 179 days. Sleep stages 1-4 all changed, with a significant decrease in percentage of stage 1, and a significant increase in both percentages of stage 2 and 3, and duration of stages 3 and 4 at the end of active treatment. After a 90-day follow-up period, only stage 3 sleep and sleep efficiency were no longer significantly changed compared to baseline, all other criteria showing maintenance of efficacy. Slow-wave sleep, which was increased during active treatment, decreased in the follow-up period. No serious adverse events were observed. These results suggest that, contrary to other hypnotics, zolpidem, after long-term administration, improves objective sleep parameters and may normalize a disturbed sleep architecture.