Several reports from Asian countries suggest a low prevalence of pulmonary embolism (PE) and deep venous thrombosis (DVT) in Asians, and sparse US data show that a slightly higher prevalence of PE/DVT in "nonwhites" than in whites is evident in all geographic regions except the Pacific region (California, Oregon, and Washington) where "nonwhites" include a larger proportion of Asians and Hispanics than in other US locations. We prospectively studied PE/DVT hospitalizations in 128,934 persons in relation to traits determined at health examinations in 1978 to 1985. Through 1994, 337 persons were subsequently hospitalized for PE and/or DVT (for PE first, n = 206). Cox proportional-hazards models with 9 covariates were used. In multivariate models, the following RRs (95% confidence intervals) were found for PE/DVT combined: black/white = 1.1 (0.4 to 1.4); Hispanic/white = 0.7 (0.3 to 1.5); and Asian/white = 0.2 (0.1 to 0. 5; p = 0.002). The lower risk of Asians was present in each sex and for persons first hospitalized for either PE or DVT. Covariates with significant positive relations to risk were age, male sex, body mass index, and a composite coronary disease risk/symptom variable; covariates not significantly related were education, marital status, smoking, and alcohol. These data suggest that Asians have very low risk of PE/DVT, which may account for US geographic variations in white/non-white risk differences. Possible explanations include the absence of hazardous mutations or unspecified PE/DVT protective traits in Asians.