BACKGROUND: Some cross-sectional studies have established an association between the morphological change of visceral adipocyte and insulin resistance. This study was undertaken to investigate the differences of the morphological change of visceral adipocyte and myostatin expressions according to insulin resistance. METHODS: Thirty four patients who underwent elective abdominal surgery were enrolled. Patients were classified into either normal glucose tolerance (NGT) group, impaired fasting glucose (IFG) group, or type 2 DM (DM) group. Adipose tissue was obtained from omental fat deposits. Morphological changes of visceral adipocyte were examined through light and electron microscopy. Real-time quantitative PCR was performed to compare the mRNA expression level of myostatin in obtained adipose tissue among NGT, IFG and type 2 DM patients. RESULTS: Mean visceral adipocyte size (microm2) was larger in IFG and DM than those with NGT. Log-transformed mean visceral adipocyte size was significantly associated with insulin resistance (P < 0.05) even after controlling for the effect of age, sex, BMI and visceral fat area. Infiltration of macrophages was more frequently observed around the visceral adipocyte of IFG and DM group compared to the NGT group. The adipocytes surrounded by macrophages showed the features of apoptosis such as chromatin condensation rather than necrosis. mRNA expression level of myostatin was not significantly different between NGT patients and patients with abnormal glucose metabolism. CONCLUSION: Enlarged visceral adipocyte and apoptotic adipocyte death appear to be a causative factor for development of type 2 DM by inducing infiltration of macrophage, although the mechanism is still unclear.