An insulin-dependent Diabetes Mellitus Registry has been developed in Allegheny County, Pennsylvania, through hospital record review and surveillance of pediatric practices. The yearly incidence ranged from 10/100,000 for nonwhite males to 16/100,000 for white males. There were no temporal trends in incidence for 1965-1976 nor major sex differences. Nonwhites had a slightly lower incidence, primarily in the younger age groups.