Twenty-four males suffering from sleep apnea syndrome were given a trial on a mechanical appliance, the Tongue Retaining Device (TRD), as a first treatment. Other treatments, behavioral or surgical, were added as needed over a period of a year, after which 2 nights of evaluation (with and without TRD) were used to test the efficacy of the TRD vs other treatments. Post-treatment the severity, as measured by the Apnea + Hypopnea Index (A + HI) on the night with the TRD, was significantly lower than either the pre-treatment or the post-treatment non-TRD night index. A disciminant function analysis including the initial difference in apnea severity associated with different sleep positions, initial weight and per cent obesity successfully predicted the treatment outcome in 20 patients (83%). It appears that the TRD can be used alone or in conjunction with other treatments to improve nocturnal respiration of patients with a wide range of apnea severity, provided that the level of this disorder is more severe when the patient sleeps in the supine position and his body weight is not greater than 50% above the ideal. © 1988.