The purpose of this study was to examine the efficacy and adverse effects of zopiclone in Thai psychiatric patients. Thirty-two insomniac outpatients with a variety of diagnoses participated in this study. Zopiclone at the dose of 7.5-15 mg was administered 15 minutes before bedtime. The sleep-questionnaire items included: 1) sleep induction; 2) duration of sleep; 3) number of awakenings, 4) sleep quality; 5) dream incidence; and 6) condition in the morning. The mean scores of each item were compared by using pair t-test. One week after treatment, significant improvement was found in all items, except item 5. In comparison between sleep at 1 week and 3 weeks after treatment, further improvement was still found in the first three items. The adverse effects found were bitter taste, drowsiness, and headache. In conclusion, zopiclone is an effective hypnotic with few adverse effects.