AIM: To evaluate the prognosis of type Ⅱ diabetes mellitus (T2DM) after gastrectomy and related factors in gastric cancer patients. METHODS: 403 gastric cancer patients with T2DM were studied, who underwent gastrectomy between May 2003 and September 2009. A review of medica records and telephone interviews was performed in this cross-sectional study. The factors included in the statistical analysis were as follows: gender, age, type of surgery, preoperative body mass index (BMI), current BMI, BMI reduction ratio, preoperative insulin or oral diabetic medicine requirement, follow-up duration, and current state of diabetes. Assessment of diabetes status after surgery was classified into four categories according to the change in hypoglycemic agents after surgery and present status of T2DM: resolution, improvement, same, and worse.(± 20.6 mo), preoperative BMI was 24.7 kg/m2 (± 3.0 kg/m2), and BMI reduction ratio was 9.8% (± 8.6%). After surgery, T2DM was cured in 58 patients (15.1%) and was improved in 117 patients (30.4%). According to the type of surgery, the BMI reduction ratio was signif icantly higher in the total gastrectomy and Roux-en-Y reconstruction group [14.2% ± 9.2% vs 9.2% ± 7.7% (Billroth Ⅱ group), P < 0.001] and signif icantly lower in the subtotal gastrectomy and Billroth Ⅰ reconstruction group [7.6% ± 8.0%, 9.2% ± 7.7% (Billroth Ⅱ group), P < 0.001]. The BMI reduction ratio, follow-up duration after surgery, type of surgery, extent of gastrectomy, and performance of duodenal bypass were signif icantly correlated to the course of T2DM (P < 0.05). The BMI reduction ratio was the most influential factor on T2DM status. In a subgroup analysis of patients with a BMI reduction ratio of 10% or less (n = 206), T2DM was cured in 15 (7.6%) patients and was improved in 57 (28.8%) patients after surgery, and only the duration of surgery was signif icantly correlated to T2DM status (P = 0.022). AIM: To evaluate the prognosis of type Ⅱ diabetes mellitus (T2DM) after gastrectomy and related factors in gastric cancer patients. METHODS: 403 gastric cancer patients with T2DM were studied, who underwent gastrectomy between May 2003 and September 2009. A review of medicament records and telephone interviews was performed in this cross-sectional study. The factors included in the statistical analysis were as follows: gender, age, type of surgery, preoperative body mass index (BMI), current BMI, BMI reduction ratio, preoperative insulin or oral diabetic medicine requirement, follow-up duration, and current state of diabetes. Assessment of diabetes status after surgery was classified into four categories according to the change in hypoglycemic agents after surgery and present status of T2DM: resolution, improvement, same, and worse. The preoperative BMI was 24.7 kg / m2 (± 3.0 kg / m2) and the BMI reduction rate was 9.8% (± 8.6%). After surgery, T2DM was cured in 58 patients (15.1% and was improved in 117 patients (30.4%). According to the type of surgery, the BMI reduction ratio was signif icantly higher in the total gastrectomy and Roux-en-Y reconstruction group [14.2% ± 9.2% vs 9.2% ± 7.7% (Billroth Ⅱ group, P <0.001) and signif icantly lower in the subtotal gastrectomy and Billroth Ⅰ reconstruction group [7.6% ± 8.0%, 9.2% ± 7.7% (Billroth Ⅱ group), P <0.001] , follow-up duration after surgery, type of surgery, extent of gastrectomy, and performance of duodenal bypass were signif icantly correlated to the course of T2DM (P <0.05). The BMI reduction ratio was the most influential factor on T2DM status. In a subgroup analysis of patients with a BMI reduction ratio of 10% or less (n = 206), T2DM was cured in 15 (7.6%) patients and was improved in 57 (28.8%) patients after surgery, and only the duration of surgery was signif icantly correlated to T2DM status (P = 0.022).