To investigate the long-term outcome of therapy and clinical symptoms of patients with OSAS (obstructive sleep apnea syndrome) in Japan, we studied 34 patients with OSAS who had been diagnosed by standard polysomnography more than one years (36.0 +/- 19.7 months: mean +/- SD) previously. They were 53.8 +/- 10.5 years old, body mass index was 27.8 +/- 5.2 kg/m2, and AHI (apnea & hypopnea index) was 50.0 +/- 24.2/h. The subjects had achieved weight loss (p less than 0.01), but had regained their initial weight at our follow-up. Eleven patients with OSAS were initially candidates for NCPAP (nasal continuous positive airway pressure), but only 5 patients used it for a prolonged time. The other 6 patients with OSAS could not use NCPAP because they did not wish to purchase a NCPAP instrument. One of 5 patients who used NCPAP for a long time died from lung cancer; thus, 4 patients used NCPAP continuously. Ten patients were commenced on ACZ (acetazolamide); however, only 5 patients took it continuously. ACZ resulted in some improvements in the sleep parameters (AHI index, desaturation time below SaO2 90%), but apnea & hypopnea duration and the difference in transcutaneous PCO2 between wake and sleep were not significantly improved by ACZ administration. ACZ was not as effective as NCPAP. Almost 60% of patients with OSAS had excessive daytime sleepiness. Hypertension was detected in about 60% of patients. Nine of 25 patients who had an automobile license had had more than one automobile accident. Nine patients who had had more than one automobile accident showed AHI greater than or equal to 30 in our study.(ABSTRACT TRUNCATED AT 250 WORDS)