Although marked differences in anthropometric characteristics and malignant lymphoma (ML) incidence suggest that the association between obesity and ML risk in Asian and non-Asian populations may differ, few studies have investigated this association in Asian populations. Here, we conducted a sex- and age-matched case-control study in a Japanese population using 782 cases and 3,910 noncancer controls in the hospital-based Epidemiological Research Program at Aichi Cancer Center Hospital. Odds ratios (ORs) and 95% confidence intervals (CIs) for anthropometric characteristics were estimated using a conditional logistic regression model that incorporated smoking and alcohol intake. Recent body weight and body mass index (BMI) showed marginally significant association with ML risk (ORs [95% CIs] per 5-unit increase in recent weight and BMI; 1.04 [0.99-1.09] and 1.11 [0.98-1.27], respectively). On the other hand, weight and BMI in early adulthood exhibited a strong association with ML risk (ORs [95% CIs] per 5-unit increase in early adulthood weight and BMI; 1.11 [1.05-1.18] and 1.33 [1.13-1.55], respectively). Further, in women, a BMI of 25.0-29.9 kg/m(2), defined as obesity in Asian populations, during early adulthood was significantly associated with ML risk compared to the normal range of 18.5-22.9 kg/m(2). By histological ML subtype, the point estimates of ORs for obesity relative to normal weight in early adulthood were over unity for non-Hodgkin lymphoma (NHL) as a whole and significant for diffuse large B-cell lymphoma (DLBCL). In conclusion, our study in Japanese subjects suggested that early adulthood obesity is associated with the risk of NHL, particularly DLBCL.