Among all the sleep-related respiratory disorders, sleep apnoea is clinically the most important one because of its high incidence and potential cardiovascular sequelae. Treatment depends upon the risk profile of the individual patient; in severe cases or in risk patients nasal continuous superpressure ventilation is employed, whereas in milder cases theophylline has been successfully used alongside general measures. 103 patients were followed up during treatment on an outpatient basis for 2 to maximum 12 months. Initially a significant reduction of the apnoea index by a 50% average was achieved. This therapeutical effect remained largely constant with a slight average deterioration at the end of the observation period, whereas the subjective feeling tone also improved in most patients. The treatment course was prematurely discontinued in 34 patients. Good to very good success was achieved in a total of 43 patients, whereas 26 patients were non-responders either initially or as the treatment proceeded. Even though theophylline treatment is now well-tried in mild forms of sleep apnoea, predictors for its use in certain groups of patients must be determined before treatment is initiated.