Introduction. Psoriatic arthritis (PsA) is an inflammatory disease of the joints, enthesis and spine associated with psoriasis. Objective of the study. To evaluate the significance of inflammatory back pain (IBP), HLA-B27, and active sacroiliitis (ASI) confirmed by magnetic resonance imaging (MRI) for the early diagnosis of PsA. Material and Methods. The study included 29 patients with PsA 16 females and 13 males (average age 41,5). Presence of IBP according to the criteria ASAS, HLA-B27 and ASI signs on the MRI dates (bone marrow edema/osteitis). Calculated DAS28 (disease activity), the Yule coefficients of association (Q: level from -1 to +1) and Phi was calculated. Results. In patients with PsA, ASI was detected by MRI significantly 41,4%. No correlation between the presence of ASI and DAS28. IBP was detected in 11 (38,6%) of 29 patients; it was longterm in 7 (63,6%) and episodic in 4 (36,4%) of patients. HLA-B27 was detected in 10 (34,5%) of 29 patients. In patients with PsA a very high level of association between ASI and IBP (Q = 0,87, Phi = 0,71) and between ASI and HLA-B27 (Q = 0,83, Phi = 0,71) was detected. Conclusion. ASI is detected by MRI significantly in patients with PsA. In patients with PsA, ASI is closely associated with IBP and HLA-B27. This fact can be used for differential diagnosis of PsA and rheumatoid arthritis. The activity level of arthritis doesn't affect detectability of ASI by MRI in patients with PsA.