Sex hormones are implicated in the immune response, with estrogens as enhancers at least of the humoral immunity and androgens and progesterone as natural immune-suppressors. In male rheumatoid arthritis (RA) patients, androgen replacement seems to ameliorate the disease and supports their involvement in the pathophysiology of the disease. The combination of androgens with cyclosporin A or methotrexate has been found to potentiate the apoptosis of monocytic inflammatory cells as well as to reduce the cell growth at least in vitro. Considerable interest has been devoted in the last years as to whether the use of oral contraceptive pills (OCs) may have a protective effect on the risk of RA. The results of many controlled studies have been found contradictory. At the present time, no consensus has been achieved regarding OCs administration and its relationship to the prevention or development of RA. In addition, an association of estrogen receptor gene polymorphism with age at onset of RA has been observed and might further explain inter-individual clinical and therapeutical-response variations. Local increased estrogen concentrations and decreased androgen levels have been observed in RA synovial fluids and seem to play a more important role in the immune/inflammatory local response.