A compact portable sensing system (PSS) was developed for home monitoring of patients with obstructive sleep apnea treated with nasal continuous positive-airway pressure (CPAP). The system consisted of a solid-state pressure sensor connected with plastic tubing to the side port of the nasal CPAP mask, a power supply, and a strip chart recorder. The device was validated against standard polysomnography in ten patients with obstructive sleep apnea undergoing overnight nasal CPAP trials. A total of 397 apneas and hypopneas were observed in the ten patients. The PSS device detected 386 events (sensitivity, 97.2 percent). In addition, there were 29 false positive events noted by the device (positive predictive value, 93 percent). The device was then tested at home in 23 patients on nasal CPAP. Eight of these patients had persistent apneas requiring adjustment of their CPAP pressure. The PSS device allowed for accurate reevaluation of nasal CPAP settings in the patient's home without necessitating expensive, time-consuming in-hospital laboratory polysomnographic studies.