Altered serum prolactin (PRL) levels have been reported in autoimmune diseases; however, data of serum PRL concentrations in rheumatoid arthritis (RA) are contradictory. We evaluated the PRL status in men affected by RA and the possible relationships among serum PRL levels, bone mass, and disease activity. We investigated 29 men affected by RA and 30 age- and sex-matched controls. All patients were evaluated for serum PRL levels, parameters of disease activity, and bone mineral density (BMD) at L2-L4 and the femoral neck. Serum PRL levels were found significantly higher in men with RA than in controls (p = 0.001). High serum PRL levels were significantly correlated with duration of RA and some laboratory parameters of RA disease activity. A negative correlation between femoral BMD and serum PRL levels were found (r = -0.821, p = 0.001). Male patients affected by RA showed high serum PRL levels. The serum PRL concentration was found to be increased in relation to the duration and the activity of the disease. Serum PRL levels do not seem to have any relationship with the BMD, at least in RA.