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We determined whether insulin therapy changes liver fat content (LFAT) or hepatic insulin sensitivity in type 2 diabetes. Fourteen patients with type 2 diabetes (age 51 ± 2 yr, body mass index 33.1 ± 1.4 kg/m2) treated with metformin alone received additional basal insulin for 7 mo. Liver fat (proton magnetic resonance spectroscopy), fat distribution (MRI), fat-free and fat mass, and whole body and hepatic insulin sensitivity (6-h euglycemic hyperinsulinemic clamp combined with infusion of [3-3H]glucose) were measured. The insulin dose averaged 75 ± 10 IU/day (0.69 ± 0.08 IU/kg, range 24–132 IU/day). Glycosylated hemoglobin A1c(Hb A1c) decreased from 8.9 ± 0.3 to 7.4 ± 0.2% ( P < 0.001). Whole body insulin sensitivity increased from 2.21 ± 0.38 to 3.08 ± 0.40 mg/kg fat-free mass (FFM)·min ( P < 0.05). This improvement could be attributed to enhanced suppression of hepatic glucose production (HGP) by insulin (HGP 1.04 ± 0.28 vs. 0.21 ± 0.19 mg/kg FFM·min, P < 0.01). The percent suppression of HGP by insulin increased from 72 ± 8 to 105 ± 11% ( P < 0.01). LFAT decreased from 17 ± 3 to 14 ± 3% ( P < 0.05). The change in LFAT was significantly correlated with that in hepatic insulin sensitivity ( r = 0.56, P < 0.05). Body weight increased by 3.0 ± 1.1 kg ( P < 0.05). Of this, 83% was due to an increase in fat-free mass ( P < 0.01). Fat distribution and serum adiponectin concentrations remained unchanged while serum free fatty acids decreased significantly. Conclusions: insulin therapy improves hepatic insulin sensitivity and slightly but significantly reduces liver fat content, independent of serum adiponectin.