Context: Chronic starvation is characterized by GH resistance, and obesity is characterized by decreased GH secretion. In both extremes, IGF1 levels may be low and androgen levels may be abnormal. Objective: To investigate the determinants of IGF1 and GH across the weight spectrum in women. Design: Cross-sectional study. Setting: Clinical research center. Study participants: In total, 32 women had participated in the study: 11 women with anorexia nervosa (AN), 11 normal-weight women, and 10 obese women of comparable mean age. Intervention: None. Main outcome measures: Pooled hourly overnight serum samples assayed for IGF1, GH, estradiol (E2), testosterone, SHBG, insulin, free fatty acids, and trunk fat. Results: Free testosterone was higher in obese women and lower in women with AN than in normalweight women, and was the only independent (and positive) predictor of IGF1 levels, accounting for 14% of the variability (P=0.032) in the group as a whole. This relationship was stronger when obese women were excluded, with free testosterone accounting for 36% of the variability (P=0.003). Trunk fat accounted for 49% of the variability (P<0.0001) of GH, with an additional 7% of the variability attributable to E2 (P=0.042) in the group as a whole, but was not a significant determinant of GH secretion when obese women were excluded. Conclusions: Free testosterone is a significant determinant of IGF1 levels in women across the body weight spectrum. In contrast, GH secretion is differentially regulated at the extremes of the weight spectrum. © 2010 European Society of Endocrinology.