This thesis examined the incidence and temporal trends of Type 1 diabetes diagnosed in Northern Ireland children using data from the Northern Ireland Childhood Diabetes Register (NICDR). Overall, there was evidence of a departure from linearity in incidence with indications that rates are levelling off in recent years. Further analyses also indicated that birth cohort effects were evident in the incidence rates suggesting that exposures in early life may play an aetiological role in this condition. A systematic review and meta-analyses was performed in this thesis to investigate the association of childhood vaccinations and subsequent risk of Type 1 diabetes. Twelve studies investigating a range of vaccinations were included. Results provided no evidence to suggest an association between childhood vaccinations and risk of Type 1 diabetes. A study using data from the Clinical Practice Research Datalink (CPRD) was included in this thesis to report findings on depression and other complications in young people diagnosed with Type 1 diabetes. This study found that rates of depression were significantly higher in cases with diabetes compared to controls without diabetes. Results also showed elevated rates of microvascular complications and significantly higher rates of cardiovascular disease compared to matched controls. Another focus of this thesis was on mortality in individuals with Type 1 diabetes. Population-based studies reporting relative mortality in Type 1 diabetes diagnosed in young people were systematically reviewed. In total, 23 independent studies were included. Associations between relative mortality and study/ country characteristics were explored. In addition to this review, a further two UK-based studies were performed to investigate mortality, one using data from the NICDR and the other using the CPRD. Both studies found excess mortality rates in individuals with Type 1 diabetes when compared, respectively, to the general population and to a group of controls without diabetes.