To investigate the frequency and etiology of diabetic osteopenia, we measured spinal bone mineral density (SBMD), total body bone mineral density (TBBMD), total body fat and lean body mass in 69 female diabetic patients (14 IDDMs and 55 NIDDMs). SBMD decreased with age in both IDDM and NIDDM, but when expressed as a percentage of age-matched normal Japanese females, some had lower SEMD, but others had normal or increased SBMD. Postmenopausal IDDM patients had lower SBMD than postmenopausal NIDDM patients. Thirteen out of 69 (18.8%) had an SBMD lower than 90% of age-matched controls. SBMD correlated positively with TBBMD. Those with lower SBMD had poor glycemic control, but there was no relation between SBMD and either duration of diabetes or presence of retinopathy and/or nephropathy. IDDM patients had lower 1.25 (OH)2D, osteocalcin than NIDDMs. SBMD correlated negatively with urinary pyridinoline and deoxypyridinoline excretion. SBMD correlated positively with body weight, and those with lower SBMD had significantly lower body mass index, body weight, fat weight and lean body mass than those with normal or increased SBMD. These results suggest that IDDM patients may be at higher risk of losing bone postmenopausally, and diabetic patients with lower SBMD have characteristics of poor diabetic control, lean habitus, low serum 1.25 (OH)2D.