['To investigate the relationship between human leptin receptor (LEPR) gene G3057A polymorphism and type 2 diabetes mellitus (T2DM) patients complicated with or without non-alcoholic fatty liver disease (NAFLD).', 'Two hundred and sixteen cases of newly diagnosed T2DM patients (104 cases complicated with NAFLD) and 108 cases of normal glucose tolerances (NGT) were recruited. Hemi-nested polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) and PCR-direct sequence analysis were conducted to detect the polymorphism of LEPR G3057A variation. Plasma leptin levels were measured by enzyme-linked immunosorbent assay kit. Plasma lipid and glucose metabolic parameters were measured routinely. Liver ultrasound was carried out for all subjects.', 'T2DM patients complicated with NAFLD had higher plasma insulin, leptin, triglycerides (TG) and low-density lipoprotein cholesterol (LDL-C) levels than those without NAFLD and NGT subjects. The variant frequency at nucleotide 3057 G-->A transversion was 76.0% in type 2 diabetic patients complicated with NAFLD, which was also significantly higher than those without NAFLD (62.1%) and NGT cases (53.2%). There was also significant difference in genotype distribution between the three groups (chi(2) = 14.63, P < 0.01).'] Is polymorphism of human leptin receptor gene associated with type 2 diabetic patients complicated with non-alcoholic fatty liver disease in China?