Objective: To examine the relationships between birthweight, current size, and fasting glucose and fasting insulin levels in Aboriginal adolescents. Design, participants and setting: Longitudinal prospective study of a Northern Territory Aboriginal birth cohort of 686. Aboriginal babies born at the Royal Darwin Hospital between January 1987 and March 1990, and followed up between December 2006 and January 2008 in over 40. NT locations. Main outcome measures: Fasting insulin and glucose levels, adjusted for gestational age, sex and contemporary age. Results: Among the 134 participants with complete data, those with fetal growth restriction (FGR) or low birthweight (LBW) at birth were not overweight at 18 years. In these circumstances, birthweight showed a significant positively directed association with fasting glucose levels (P = 0.002). Current weight showed a significant and positively directed association with both fasting insulin (P< 0.001) and fasting glucose levels (P= 0.001), and current height showed a significant and positively directed association with insulin levels (P =0.006). Conclusions: Birthweight was only positively associated with fasting glucose levels, with no association with fasting insulin levels. The high-risk combination for type 2 diabetes of LBW or FGR with later overweight or obesity was rare in this adolescent Aboriginal population.