Peroxisome proliferator‐activated receptor γ (PPARγ) controls adipocyte differentiation and regulates lipid and glucose homeostasis. Therefore, the PPARγ gene may affect insulin sensitivity and resistance. We analyzed the relationship between C/T exon 6 polymorphism of the PPARγ gene and various clinical parameters in type 2 diabetic patients. There were no significant differences in the frequencies of genotype and allele between diabetic patients with and without nephropathy. Diabetic patients were divided into two groups: patients bearing at least one T allele (CT/TT), and patients with no T allele (CC). Levels of serum triglyceride and body mass index (BMI) were significantly higher in the CT/TT genotype group than in the CC genotype group. Since obesity affects insulin resistance, the diabetic patients were also divided into two groups: those with a BMI of <23, and those with a BMI of >23. In patients with a BMI of <23, there was no significant change in the levels of glycosylated hemoglobin A1c (HbA1c) between the CC and CT/TT genotype groups. However, in patients with a BMI of >23, HbA1c levels were significantly higher in the CT/TT genotype group than in the CC genotype group. It appears that the CT/TT genotype with PPARγ gene polymorphism may contribute to higher BMI and higher serum triglyceride and HbA1c levels in Japanese type 2 diabetic patients. J. Clin. Lab. Anal. 18:317–321, 2004. © 2004 Wiley‐Liss, Inc.