Idiopathic osteoporosis in men is associated with significant morbidity and mortality. It is believed to be associated with perturbations in the growth hormone -Insulin-like Growth Factor (GH-IGF-1) axis. Our study of 28 men, representing 3 different bone mineral density (BMD) groups confirmed previously reported observations of a significantly reduced serum IGF-1 with reduced BMD (p=0.009). In addition, physiological and pharmacological stimulation of the GH-IGF axis revealed comparable GH synthesis across the BMD groups. This was suggestive of GH resistance at the hepatic or skeletal level in the low BMD group. An IGF-1 generation test, where recombinant human GH (rhGH) was administered to the subjects failed to show significant group differences in IGF-1 production. In addition, there was no evidence of a reduced bone marker response to rhGH in the low BMD group. The suggested resistance to GH was not demonstrated in the low BMD group. Low birthweight in females has also been demonstrated to be associated with increased intestinal calcium adsorption and increased serum 1, 25 (OH)₂ vitamin D. This suggested that an up-regulation of vitamin D occurred to promote calcium adsorption in the poor in utero environment. Our study of 149 men representing different birthweight groups failed to demonstrate either increased intestinal calcium adsorption or increased serum 1, 25 (OH)₂ vitamin D in the low birthweight group. Interestingly, 122 men who had previous DEXA scans demonstrated a significant association between femoral neck BMD and intestinal calcium adsorption (r = 0.2, p < 0.01).