It is common to find monoclonal gammopathy in the investigation workout for an unrelated disorder. There are studies relating rheumatic diseases and therapies which show an increased risk of monoclonal gammopathy. The specific mechanisms are not well understood but chronic antigen stimulation assumes an important role. Specific rheumatic diseases have consistently been associated with lymphoproliferative disorders but less attention has been paid to the possible association between monoclonal gammopathy of undetermined significance and multiple myeloma. We reviewed previous studies regarding monoclonal gammopathy and different rheumatic diseases and treatments associated focusing on prevalence, risk factors and possible pathogenic mechanisms. The clinical approach of a monoclonal gammopathy and its follow-up are explained.