Limited data are available on the vitamin D3 status and bone mineral density (BMD) of patients with psoriasis or with psoriatic arthritis. Our study intended to explore possible correlations between vitamin D status and BMD, as well as among these parameters and the features of the underlying disorder. Seventy-two patients with psoriasis/or psoriatic arthritis (female : male ratio, 40:32; mean age, 58.5 ± 11.6 years; mean duration of follow up, 142.7 ± 147.7 months) participated in the study. We evaluated the characteristic clinical features of the underlying disease, performed bone densitometry of the lumbar spine and the hip region, measured the serum vitamin 25(OH)D3 levels of the patients, and undertook the statistical analysis of the relationships between the clinical and the laboratory parameters. The proportion of patients with a low BMD value did not exceed that seen in the general population. We found an inverse correlation between the serum level of vitamin 25(OH)D3 and body mass index, as well as between the former and the severity of skin involvement. Furthermore, the activity of psoriatic arthritis was significantly higher in patients with inadequate vitamin D3 status. In patients with psoriatic arthritis, BMD significantly exceeded the values measured in patients suffering from psoriatic skin lesions only. Our findings suggest the importance of evaluating the vitamin D3 status and screening for comorbid conditions in patients with psoriasis or psoriatic arthritis. This appears justified, in particular, due to the possible role of hypovitaminosis D3 in provoking the development of skin lesions and joint symptoms.