The objectives of this prospective cross-sectional study are to determine allele frequencies, linkage-disequilibrium structure and transferability of NPC1 polymorphisms previously reported to be associated with morbid-adult obesity or diabetes independent of body weight, and to determine whether these NPC1 polymorphisms are associated with metabolic disease phenotypes in an ethnically diverse New Mexican obstetric population. The gene discussed is NPC1; the disease is diabetes mellitus.