Aim <p>To analyze sex differences in age trajectories of supine positional obstructive sleep apnea (POSA).</p> Methods <p>We conducted retrospective analysis of polysomnography studies from 13,144 individuals aged from 2 to 103 years with at least 30&#xa0;min of both supine and lateral sleep. We used generalized linear mixed-effects models to estimate position-specific mean apnea-hypopnea index (AHI) values and logistic regression to estimate the proportion with POSA or with exclusive POSA among individuals with obstructive sleep apnea (OSA). Predictors included sex, 5-y age group, sleep position, and their interactions.</p> Results <p>Supine AHI was higher than lateral AHI regardless of age or sex except under age 5 y. The ratio of supine AHI to lateral AHI reliably exceeded 2 after age 30–35 in males and age 50–55 in females. For both sexes, the proportion with POSA among individuals with OSA increased rapidly with age until 30–35 and then stabilized. The proportion with POSA among individuals with OSA was significantly higher in males than females for each age group between 40 and 75 (<i>p</i> &lt; 0.03). Among individuals with OSA in those 20 and older, the proportion with POSA was 64.6% (95% CI: 62.7%, 66.5%) in males and 55.8% (95% CI: 53.6%, 57.8%) in females. The proportion of individuals showing exclusive POSA also increased with age and peaked near 41% at age 15–20 in males and at age 20–25 in females.</p> Conclusion <p>POSA becomes more common with age in both sexes; in women, its prevalence is generally lower but continues to increase after age 65.</p>