In 1,150 patients with sleep apnea syndrome, the apnea number, the morning theophyllin level, the symptom of morning exhaustion were recorded for the first night of theophyllin therapy and in the follow-up period of up to 5 years; in addition, side effects were noted at the end of the observation period. Prior to start of the therapy, the average apnea number was 97 per night; this decreased to 25 per night in the initial therapy. In the observation period of between 3 and 28 months, the number of apnea phases increased slightly on average. The symptoms of morning exhaustion initially decreased to 60% but increased again by about 20% over the next five years. In responders, theophyllin reduces the number of apnea in the long term course; however, frequent therapy controls are needed to determine the optimal dosage. Longitudinally, patients with an apnea index < 20/profited most from this drug therapy.