The "New World syndrome" is comprised of disorders that are hypothesized to have resulted from an interaction of the Amerindian genotype with an environment that includes marked changes in lifestyle and diet. The principal component of the syndrome is adult-onset (noninsulin dependent) diabetes mellitus. The purpose of this paper is to describe the emergence of diabetes in a Mexican-origin population. Using a unique file of multiple-cause mortality data, we have computed standardized mortality ratios and relative standardized mortality ratios for Mexican-origin individuals and for other white persons age 30 and over from the 1930's through the middle 1980's. Results for the study population residing in Bexar County (San Antonio), Texas, show that diabetes mortality for Mexican-origin individuals did indeed increase in a pattern consistent with the New World syndrome hypothesis. This study is the first description of the emergence of diabetes using a data set with consistently defined causes of death and demographic characteristics.