Prolactin (PRL) is a hormone synthesized and secreted by lactotroph cells in the anterior pituitary gland. There is also extrapituitary hormone secretion by many cells, including cells of the immune system. In physiological conditions PRL is responsible for lactogenesis and other processes associated with it. PRL plays a significant role during the immune response as a cytokine, affecting proliferation and differentiation of many immune system cells. The biological effect of the hormone depends on binding with the specific prolactin receptor PRL-R, and activation of the transcription factors of targeted genes. For T lymphocyte stimulated PRL, that factor is mainly the interferon regulatory factor (IRF-1), which gives the possibility of adjusting the prolactin immune response. Literature data indicate that hyperprolactinemia (HPRL) is one of the important factors in the pathogenesis and course of autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis and Sjogren's syndrome. HPRL is diagnosed in nearly one-third of these patients. However, only a few data indicate the role of prolactin in psoriatic arthritis (PsA), whose etiology and disease progression are not fully elucidated, and the diagnosis is very difficult. Currently there is indicated a pronounced connection between the course of HPRL and activity of PsA. It seems also to be interesting that, regardless of the PRL levels in serum of patients with PsA, administration of bromocriptine--drug-lowering hormone--improves joint and skin symptoms, which indicates a decrease in disease activity, and is a promising way of alternative therapy for psoriatic arthritis. However, the effect of PRL on the pathogenesis and the severity of psoriatic arthritis has not yet been fully understood and further research will provide a possibility to assess the prognostic and diagnostic significance of prolactin in patients with PsA.