Lymphoproliferative disorders and autoimmune diseases have some common aspects in their clinical appearance. We reviewed 940 patient charts with malignant lymphomas to assess the rate of associated autoimmune diseases. Of 421 non-Hodgkin's lymphoma (NHL) patients (230 males, 191 females), 32 (7.6%) had an autoimmune disease (26 females, six males, mean age 48.3 years). The most common diagnosis was Sjögren's syndrome. The other cases were autoimmune skin diseases (5), thyroiditis (3), polymyositis (2), scleroderma (2), other musculoskeletal disorders (2), rheumatoid arthritis (1), vasculitis (1), undifferentiated collagenosis (1), colitis ulcerosa (1), autoimmune hepatitis (1), Addison's disease (1), and autoimmune hemolytic anemia (1). Of 519 Hodgkin's lymphoma patients (308 males, 211 females), an associated autoimmune disease occurred in 45 (8.6%) (25 females, 20 males, mean age 39.2 years). In 31 cases, we found autoimmune thyroid disorders, then came glomerulonephritis (3), immune thrombocytopenia (3), insulin-dependent diabetes mellitus (2), autoimmune hemolytic anemia (1), seronegative spondylarthritis (1), systemic lupus erythematosus (1), mixed connective tissue disease (1), scleroderma (1), and vasculitis (1). We also analyzed histology, choice of treatment, and sequence of appearance of the disease types. We found a difference between NHL and Hodgkin's lymphoma patients, since in NHL autoimmunity - mostly from Sjögren's syndrome - preceded the lymphoma diagnosis (70%), but in Hodgkin's the autoimmunity developed mainly after the treatment of malignancy. The relatively high prevalence of autoimmune diseases in malignant lymphomas has several explanations. Clinicians have to consider autoimmunity when treating lymphoproliferative disorders.