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 using a 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