Factors associated with increased severity of sleep apnea; obesity, the supine sleep posture, and age, were tested for their association with the effectiveness of the Tongue Retaining Device (TRD) for the control of the apneic events in a group of 16 male patients. Sixty-nine percent of the patients (11 of 16) were successful with this treatment. The strongest predictor of this success was the presence of an increased severity associated with the supine sleep posture. Patients with substantial worsening of apnea index while in the supine sleep position were more responsive to the TRD than those who were equally affected in both sleep positions. A discriminant function analysis that entered age, obesity, and the ratio of apneas per hour in side v back sleep posture correctly classified the success of patients' response to this treatment.