This study investigates the effects of diet-induced changes in maternal body condition on glucose tolerance in sheep. Welsh Mountain ewes were established, by dietary manipulation, at a body condition score of 2 (lower body condition LBCS, n = 17) or >3 (higher body condition HBCS, n = 19) prior to and during pregnancy. Birth weight and postnatal growth were similar in LBCS and HBCS offspring. In young adulthood, LBCS offspring had increased fasting glucose levels (3.8 +/- 0.07 vs 3.6 +/- 0.05 mM, P < .05), poorer glucose tolerance (2274 +/- 22.6 vs 2161 +/- 33 min/mM, P < .01), and reduced insulin secretion (0.58 +/- 0.05 vs 0.71 +/- 0.07 nM/min, P = .07). Increased fasting glycemia, mild glucose intolerance, and impaired initial insulin secretory response, as observed in LBCS offspring, are indictors of increased diabetes risk in humans. These findings suggest that altered maternal body composition and an imbalance between the fetal and postnatal environment influence offspring glucose tolerance.