Patients with systemic inflammatory rheumatic diseases (such as rheumatoid arthritis, lupus erythematosus, systemic sclerosis, idiopathic inflammatory myopathies, or Sjögren's syndrome) are at increased risk of cancer, including hematological malignancies (leukemias and lymphomas), as well as non-hematological cancers (e.g. lung, esophageal, prostate or ovarian cancer). This increased risk for cancer development in patients with rheumatic diseases is attributed to the immune (autoimmune) processes and the medical treatment. Due to the often similar symptoms and the occurrence of systemic paraneoplastic syndromes it is very important to evaluate the association between rheumatic diseases and cancer. This paper presents issues concerning the development of cancer in patients with rheumatic diseases and the risk of cancer associated with drugs used for the treatment of rheumatic diseases.