objective: to investigate the prevalence of obstructive sleep apnea in patients with ischemic stroke and to evaluate the effectiveness of nasal continuous positive airway pressure treatment. methods: overnight polysomnography was performed by a computerized system in 19 subjects with ischemic stroke. patients with an apnea-hypopnea index > 5 were considered to have obstructive sleep apnea. the appropriate level of continuous positive airway pressure for each patient was determined during an all-night continuous positive airway pressure determination study. attended continuous positive airway pressure titration was performed with a continuous positive airway pressure auto-titrating device. results: obstructive sleep apnea prevalence among patients with ischemic stroke was 73.7%. the minimum sao2 was significantly lower, and the percent of total sleep time in the wake stage and stage 1 sleep was significantly longer in patients with obstructive sleep apnea. in two patients with severe obstructive sleep apnea, we observed a decrease in the apnea-hypopnea index, an increase in mean wake time, mean sao2, and minimum sao2, and alterations in sleep structures with continuous positive airway pressure treatment. conclusion: as the diagnosis and treatment of obstructive sleep apnea is of particular importance in secondary stroke prevention, we suggest that the clinical assessment of obstructive sleep apnea be part of the evaluation of stroke patients in rehabilitation units, and early treatment should be started.