This study aims to evaluate the association between sleep-wake rhythm regularity and continuous positive airway pressure (CPAP) adherence. We retrospectively analyzed sleep-wake rhythms with activity monitoring and CPAP adherence among obstructive sleep apnea (OSA) patients newly diagnosed and introduced to CPAP therapy at the Sapporo Hanazono Hospital from January 2018 to June 2022. Among a total of 45 patients, 10 withdrew from CPAP therapy within a year. Nineteen were classified into the good-adherence and 16 into the poor-adherence group. No significant differences were detected among the groups in apnea-hypopnea index (AHI), sleep efficiency, or subjective sleep quality, but a difference was observed in sleep latency, with the CPAP withdrawal group showing higher variability in sleep onset and lower regularity and/or amplitude in circadian behavior activity rhythm than the good-adherence group. Our results suggest that irregularities, particularly in sleep onset, and damped sleep-wake rhythm can be risk factors for CPAP withdrawal.