Psoriatic arthritis (PsA) is a chronic, inflammatory disease. It occurs in 6 to 42% of patients suffering from psoriasis. The cause of both PsA and psoriasis is still unknown. In progressing PsA synovitis, bone erosion, osteolysis (distal phalanges, distal epiphysises of forearm and carpus bones) and new bone formation can be observed. PsA results in destructive abnormalities as well as simultaneous proliferation. The incidence of osteolytic abnormalities in iliac bone is not a typical sign of PsA. In the paper the case of a 48-year-old man, who was diagnosed with PsA 10 years earlier is presented. The patient was treated irregularly. There occured disease exacerbation, progressing devastation, decline in body mass, high inflammatory degree and osteolytic abnormalities in iliac bones that are usually associated with cancer. A wide imaging diagnosis had been carried out (KT of chest, KT of abdominal cavity, scintigraphy, PET), which did not confirm cancer development. Due to the lack of improvement during treatment with disease modifying drugs (methotrexate, cyclosporine), was decided to include biological agents for the treatment of anti TNF-α (infliximab, adalimumab).