Although children with IDDM are at a sevenfold increased risk of dying when compared with nondiabetic individuals of the same age, the factors associated with the excess in mortality remain unclear. To investigate potential determinants of mortality among IDDM patients, a case-control study was conducted. These retrospectively obtained data indicated that shorter relative height at onset, frequent diabetes-related readmissions, the presence of diabetes complications, a family history of diabetes, premature familial mortality, no participation in school team sports, and a lower level of education were related to subsequent mortality among males. Among females, however, a shorter duration of diabetes clinic attendance and the presence of diabetes complications were the only significant associations to mortality.