Obstructive sleep apnea (OSA) is a common disorder associated with multiple adverse health consequences and its prevalence is increasing in parallel with rising obesity trends. Early support for ethnic differences in OSA prevalence and severity has been derived from studies of relatively homogenous ethnic groups. However, between-study comparisons are problematic given differing methodologies. Recent large inter-ethnic studies examining different ethnic populations using standardized protocols support the notion that Chinese have an increased OSA prevalence and severity compared to those of European descent. Although the evidence is less clear, some data suggest that Hispanic/Mexican Americans also show higher rates of OSA, while OSA prevalence in African Americans is not dissimilar to that of populations of European ancestry. Of the anatomical traits underlying differences in OSA prevalence and severity between ethnic groups (i.e., obesity, fat distribution, and craniofacial structure) obesity appears to be the most important. The effect of ethnicity on non-anatomical factors (i.e., upper airway muscle responsiveness, arousal threshold, and loop gain) responsible for OSA severity and potentially prevalence is currently unknown and needs further research.