The relationship between a history of selected medical conditions and risk of lymphomas was investigated in a hospital-based case-control study conducted in Northern Italy on 429 incident, histologically confirmed cases of non-Hodgkin's lymphoma (NHL), 158 cases of Hodgkin's disease (HD) and 1157 controls admitted to hospitals for acute conditions. The odds ratios (OR) for NHL were above unity in patients with a history of infectious mononucleosis (OR 2.9), herpes zoster (OR 1.8), pyelonephritis (OR 4.9), tuberculosis (OR 1.8), malaria (OR 1.9), any chronic bacterial diseases (OR 1.7), rheumatoid arthritis (OR 1.7) and psoriasis (OR 2.5). With reference to HD, the ORs were 4.0 for infectious mononucleosis, 2.9 for herpes zoster, 3.3 for pyelonephritis, 2J for tuberculosis, 1.4 for chronic bacterial diseases, 2.4 for rheumatoid arthritis, 2.7 for psoriasis and 2.1 for diabetes. The association of NHL and HD with herpes zoster was restricted to the first ten years since the onset of the disease. The relationships between NHL and mononucleosis (OR 12.9), malaria (OR 2.8) and psoriasis (OR 14.0) were stronger for cases aged ≥ 60 years, and that with tuberculosis (OR 3.5) was stronger for younger cases. For HD, the positive association was stronger for cases aged ≥ 40 years for herpes zoster (OR 3.8) and diabetes (OR 2.6). An increased risk of NHL was found in association with poliomyelitis (OR 1.6) (restricted to cases aged ≥ 60 years, OR 4.0) and BCG immunizations (OR 1.6), but not with vaccination against smallpox, tetanus and diphtheria; increased risks of HD were found in relation to poliomyelitis and BCG immunization in cases aged ≥ 40 years (OR respectively 2.5 and 2.1), or ≥ 50 years (OR 4.3 and 2.2). Thus, our results confirm the association between a history of several chronic infectious and inflammatory diseases and the risk of NHL or HD, and are compatible with a role of chronic immunological alterations in the aetiology of lymphomas.