Previous epidemiological studies describe a positive association between body mass index (BMI) and Hodgkin's lymphoma, mainly in obese vs. normal weight individuals. We examined the shape of this relationship in individuals aged 16 years or older, using primary care data from the United Kingdom's Clinical Practice Research Datalink. Cox models were fitted with linear, non-linear (spline) and categorical BMI. Models were adjusted for potential confounders and effect modification was investigated. Five point eight two million patients were included, 927 of whom developed Hodgkin's lymphoma during 41.6 million years of follow-up. Each 5 kg/m2 increase in BMI was associated with a 10% increase in Hodgkin's lymphoma (95% confidence intervals: 2-19). Analysis of non-linearity suggested a J-shaped association with incidence increasing with BMI above 24.2 kg/m2. Seven point four per cent of adult Hodgkin's lymphoma cases were estimated to be attributable to excess weight. Our findings suggest a pattern of increasing risk beyond the World Health Organisation healthy weight category in the general population.