Anthropometric characteristics, physical activity, and risk of non-Hodgkin's lymphoma, its subtypes, and B-cell chronic lymphocytic leukemia (B-CLL) were evaluated in a prospective cohort study of 37,931 Iowa women who were aged 55-69 years at baseline in 1986. Through 1998, 261 cases of non-Hodgkin's lymphoma (137 diffuse, 58 follicular, and 32 small lymphocytic lymphomas) and 63 cases of B-CLL were identified by linkage to the Iowa Cancer Registry. Height, weight, body mass index, waist/hip ratio, and physical activity were not associated with risk of non-Hodgkin's lymphoma overall or with diffuse or follicular lymphoma in particular. After adjustment for other non-Hodgkin's lymphoma risk factors, there was an inverse association of baseline body mass index (relative risks (RRs) across quartiles: 1, 0.4, 0.4, 0.3; p trend = 0.03) with risk of small lymphocytic lymphoma. In contrast, for B-CLL there were suggestive positive associations with body mass index at age 50 years (RRs across quartiles: 1, 1.9, 1.5, 2.7; p trend = 0.03) and (more weakly) baseline body mass index (RRs across quartiles: 1, 1.1, 1.6, 1.3; p trend = 0.3). In summary, we found no evidence that height, weight, body mass, or physical activity plays an important role in non-Hodgkin's lymphoma overall or in diffuse or follicular lymphoma in particular. The opposite associations of body mass index with small lymphocytic lymphoma versus B-CLL may be a chance finding but, if confirmed, would suggest different etiologies for these malignancies.