We report nine cases of arthritis associated with a monoclonal gammapathy. Joint involvement was noted simultaneously or after the diagnosis of monoclonal gammapathy was made. The cases had oligoarthritis or polyarthritis mimicking rheumatoid arthritis. However, rheumatoid factor was absent in all patients, and distal interphalangeal joints were involved in two cases and sacroiliitis in one. The plasma cell dyscrasia was a multiple myeloma in two cases and monoclonal gammapathy of undetermined significance in the other patients. The light chain isotype was kappa in eight of our patients. A type I cryoglobulinaemia was associated in four cases; it was detected in the synovial fluid of two of them. We suggest that the occurrence of paraproteinaemia with chronic arthritis is more than a chance association. Moreover, a monoclonal gammapathy should be searched for in patients presenting with atypical seronegative arthritis.