Objectives: To assess whether patients with OSA have more severe motor, cognitive, and functional impairment at the time of admission to the rehabilitation center and to investigate whether early detection and treatment of OSA using Bi level Positive Air Pressure (BiPAP) impact the outcome of these patients after 1 month of rehabilitation treatment. Design: Single-blind prospective randomized trial. We analyzed differences intra- and intergroups at baseline and at 30 days. We used Kruskall-Wallis test, Mann-Whitney, and the Wilcoxon signed rank tests. P value<0.05 was considered significant. Setting: Stroke Unit. FLENI Rehabilitation Institute. Participants: Patients (N=40) admitted to the rehabilitation unit 2 to 8 weeks after a stroke. Interventions: We performed overnight polysomnography (PSG) in patients. Those with an apnea/hypopnea index >10 per hour were randomized to standardized 30-day rehabilitation program with or without the addition of BiPAP treatment at night. Those subjects with stroke without OSA served as controls. Main Outcomes Measures: FIM, Barthel Index (BI), Fugl-Meyer Upper Extremities (FMUE) and Lower Extremities (FMLE), Frontal Assessment Battery, Addenbrooke Cognitive Examination and Digit Span scales at baseline and at 30 days. Results: All groups showed improvements in FMUE, FMLE, FIM and BI after 30 days. The early BiPAP treatment produced significant improvements of the FMUE score (P=.05) and FMLE score (P=.019). Both groups (OSA with early BiPAP treatment and the non-OSA) showed significant increase of the ACE score after 1 month. Conclusions: Early OSA detection and BiPAP treatment improves significantly motor performance after 1 month. PSG evaluation looking for OSA should be part of the standardized evaluation of stroke patients at admission to stroke rehabilitation facilities.