BACKGROUND: The results of previous studies suggest that portion size is a major factor dictating dietary energy intake. We investigated the relationship between frequencies of rice meals, bowl volumes, and dietary energy intake in a sample of patients with type 2 diabetes. METHODS: A total of 203 type 2 diabetes patients were enrolled in the study. A one-week food diary was collected from each patient and used to assess the types of meal consumed as well as the context of consumption. The volumes of the eating vessels (rice, soup and side dish bowls) used by each patient were obtained by comparisons to measuring cylinders, and dietary energy and macronutrient intake were estimated for each patient by consulting three-day dietary records. RESULTS: The mean age of the 203 subjects (male: 76, female: 127) was 53.9 +/- 9.1 years and the average body mass index (BMI) was 25.6 +/- 4.2 kg/m2. Among the subjects who ate three times per day, 96.4% consumed rice more than twice out of three meals. The median volume of rice bowls used by patients was 350 cc, of soup bowls was 530 cc and of side dish bowls was 260 cc. Portion size, as estimated by rice bowl volume, was not associated with BMI. Male subjects tended to eat out of larger rice and soup bowls (P < 0.001). Portion size was correlated with energy intake from rice (P = 0.021), but not with total energy intake (kcal/kg/day), especially in male subjects. CONCLUSION: Portion size of rice bowl was correlated with energy intake from rice, but not with total energy intake in male subjects with type 2 diabetes. To design effective meal planning methods for patients with type 2 diabetes, further prospective studies are warranted to investigate causative relationships between portion size andmetabolic conditions as well as variation by gender.