A series of patients having onset of Type I (insulin-dependent) diabetes mellitus before age 17 years was identified from consecutive admissions to the Children's Hospital of Pittsburgh. Family history data were obtained yielding 1006 families (1085 cases) with complete information. The prevalence of diabetes among the children differed by birth order, with a greater number than expected among first born. There was also an increased prevalence among children born to mothers older than 35 years, as well as an increased prevalence among children of very young mothers. The increased prevalence of diabetes among offspring of older mothers was apparent even after life table age corrections were made. However, both the increased prevalence among first born children and the increased prevalence among children of very young mothers could be attributed to an older attained age of these children in this particular population. This indicated that the maternal age effect was present but a birth order effect was absent when age was taken into account.
