PURPOSE: To identify ethnic differences for risk of hospitalization for asthma and chronic obstructive pulmonary disease (COPD). METHODS: We undertook a cohort study with 126,019 participants: 55% whites, 27% blacks, 11% Asians, and 4% Hispanics. To estimate asthma and COPD risk, we used Cox proportional hazards models adjusted for age, sex, body mass index, education, smoking, and alcohol intake. End points were hospitalizations for asthma or COPD. RESULTS: Compared with whites, relative risks (RR) with 95% confidence intervals (95% CI) for asthma among other groups were: blacks, 1.7 (1.4-2.0); Hispanics, 0.9 (0.6-1.4); and Asians, 1.6 (1.2-2.1). Among Asians, increased risk was concentrated in Filipino men and women and South Asian men. For COPD, whites were at highest risk; RR of blacks was 0.9 (0.7-1.0); Hispanics, 0.6 (0.3- 0.9); and Asians, 0.4 (0.3-0.6). COPD risk among Asians was lowest in Chinese with RR of 0.3 (0.1-0.5). CONCLUSIONS: Ethnic disparities in risk of asthma and COPD as well as between both diseases exist, especially for Asian Americans, who have high asthma risk and low COPD risk. While residual confounding for smoking or other environmental factors could be partially responsible, genetic factors in Asians may be involved in decreased COPD risk.