The birth prevalence of Down syndrome (DS), although decreasing in parts of the world, is not known in many specific subpopulations. The rate of DS for live births was determined for a 15-year period (1974-1988) at the Los Angeles County-University of Southern California Medical Center, which is a large public hospital serving a predominantly Latino population. DS was ascertained primarily by clinical monitoring of newborn infants. The overall rate of DS was 1.60/1,000 live births and had minimal fluctuation throughout the 15 years. The rate of DS for Latino births was 1.69/1,000 live births, 1.67 when adjusted for maternal age, and 1.75 when corrected for prenatal diagnosis. The high rate of DS in the Latino population was associated with advanced maternal ages and increased maternal-age specific rates for DS, especially in the age ranges of 30 to 34 and 40 to 44 years, when compared with other studies.