Because Hispanics in the Southwest are genetically admixed with American Indians, the hypothesis has been advanced that the excess occurrence of diabetes mellitus, obesity, and gallbladder disease in this ethnic group may be genetic in origin and results from genes derived from American Indians. This report describes the prevalence of these diseases in 1,175 adult Hispanic participants in a survey of a New Mexico community conducted in 1984-1985. At nearly all ages, the majority of subjects had a body mass index of 25 kg/m2 or greater, and a substantial proportion exceeded 30 kg/m2. The prevalence of obesity was much greater in these Hispanics than is shown in nationwide data for US whites. Diabetes mellitus was also reported more often by Hispanic subjects in this survey than by US whites nationwide. A report of gallbladder trouble or of gallbladder removal was common in both males and females; the prevalence of gallbladder removal was as high in this population as in Mexican Americans previously studied in Starr County, Texas. In spite of the high prevalence of obesity, hypertension was less frequent among the New Mexico Hispanics than is shown in nationwide data for US whites. These findings complement those of previous surveys in Texas, which have shown a notably high proportion of adults to be obese, to have non-insulin-dependent diabetes mellitus, and to have gallbladder disease. The similar epidemiology of these diseases in the Hispanics of New Mexico and the Mexican Americans of Texas supports the hypothesis that American Indian admixture underlies the development of these conditions in Hispanics throughout the Southwest.