Psoriatic arthritis occurs almost exclusively together with psoriasis (of the skin). Thus, psoriasis-associated diseases or comorbidities are also seen in psoriatic arthritis patients. Among the clinically most relevant comorbidities are cardiovascular diseases and their risk factors, namely smoking, obesity and the metabolic syndrome. Moreover, psychological conditions and osteoporosis should also be considered. The link between psoriasis, psoriatic arthritis and its comorbidities has been established based on epidemiological studies; however, at least for the cardiovascular comorbidities, the association can be explained based on novel insights into the pathogenesis of atherosclerosis. For the practising physician it is important to take into account the aspect of comorbidity to come to an optimal treatment decision in each individual case. Clinical decision-making is complicated further by the fact that comorbidity necessitates comedication which again influence the choice of treatment.