The pathogenesis of diabetic osteopenia is unclear. The markers of bone metabolism may show some changes in diabetic patients. In this study, we investigated the effect of glycemic control on serum osteocalcin level and urinary hydroxyproline excretion and the relations of these markers to duration of diabetes, C-peptide status, and body mass index. Twenty-seven men with poorly controlled diabetes mellitus (DM) (HbA1>9%, fasting plasma glucose>7.8 mmol/liter) between ages 25 and 60 years (means±SD 46.6±10.4) were included in the study. Duration of diabetes was 5.8±4.7 years, body mass index (BMI) was 25.9±3.5 kg/m², and fasting C-peptide was 2.33 (1.05–3.21) μg/liter. None of the patients had a disease or were treated with drugs that would interfer with calcium or phosphate metabolism and/or bone structure. They were free from chronic diabetic complications. Of these patients, 11 were lost to follow-up before metabolic control was achieved. The remaining 16 patients obtained good glycemic control (HbA1<8.3%, fasting plasma glucose <7.8 mmol/liter) and completed the study. Serum osteocalcin level and urinary hydroxyproline eceretion were determined before and after glycemic control. Urinary hydroxyproline excretion was not significantly changed by glycemic control [17.8 (7.1–23.2) versus 18.1 (10.9–28.1) mg/m² day, P>0.05]. However, serum osteocalein level was significantly elevated (5.04±1.43 versus 4.17±1.83 μg/liter, P=0.04). We found no correlation among fasting plasma glucose, HbA1, and fasting serum C-peptide levels with urinary hydroxyproline excretion. There was also no correlation between serum osteocalcin and fasting plasma glucose or serum C-peptide, but HbA1 was negatively correlated with serum osteocalcin (P=0.01). No correlation was found between DM duration and BMI in the patients with serum osteocalcin level and urinary hydroxyproline excretion. To eliminate the possible effect of exogenous insulin on bone metabolism, the correlation analysis between the markers and C-peptide was further repeated in oral agents-treated patients. Serum C-peptide was not correlated to serum osteocalcin or urinary hydroxyproline in this subgroup of patients. Knowing that serum osteocalcin is a marker of bone formation, we concluded that osteoblast function may improve by glycemic control in diabetic patients; this may be due to correction of metabolic abnormalities associated with insulinopenia.