Nutritional status is known to alter immune function, a suspected risk factor for non-Hodgkin lymphoma (NHL). To investigate whether long-term over, or under, nutrition is associated with NHL, self-reported anthropometric data on weight and height from over 10,000 cases of NHL and 16,000 controls were pooled across 18 case-control studies identified through the International Lymphoma Epidemiology Consortium. Study-specific odds ratios (OR) were estimated using logistic regression and combined usinga random-effects model. Severe obesity, defined as BMI of 40 kg m−2 or more, was not associated with NHL overall (pooled OR = 1.00, 95% confidence interval (CI) 0.70–1.41) or the majority of NHL subtypes. An excess was however observed for diffuse large B-cell lymphoma (pooled OR = 1.80, 95% CI 1.24–2.62), although not all study-specific ORs were raised. Among the overweight (BMI 25–29.9 kg m−2) and obese (BMI 30–39.9 kg m−2), associations were elevated in some studies and decreased in others, while no association was observed among the underweight (BMI < 18.5 kg m−2). There was little suggestion of increasing ORs for NHL or its subtypes with every 5 kg m−2 rise in BMI above 18.5 kg m−2. BMI components height and weight were also examined, and the tallest men, but not women, were at marginally increased risk (pooled OR = 1.19, 95% CI 1.06–1.34). In summary, whilst we conclude that there is no evidence to support the hypothesis that obesity is a determinant of all types of NHL combined, the association between severe obesity and diffuse large B-cell lymphoma may warrant further investigation. © 2007 Wiley-Liss, Inc.