Ten male patients selected as having sleep apnea predominantly of the obstructive type associated with the supine sleep position on their evaluation night were trained for 1 additional night to avoid the back sleep position by wearing a gravity-activated position monitor/alarm on the chest. This device emitted an auditory signal if the patient remained supine for more than 15 s. The number of apneic events was significantly reduced, as were the number of episodes of significant O2 desaturation. While wearing the alarm, the apnea index of seven patients remained within or near normal limits. On a follow-up night, with only instructions to maintain the lateral decubitus posture, five patients remained significantly improved. Sleep position training may be appropriate as a single or interim treatment for a significant number of sleep apnea patients who have position-related obstruction.