Objective. To study the effect of the presence of fibromyalgia (FM) on common clinical disease activity indices in patients with psoriatic arthritis (PsA). Methods. Seventy-three consecutive outpatients with PsA (mean age 51.7 yrs; 42 females, 57.5%) were enrolled in a prospective cross-sectional study. FM was determined according to American College of Rheumatism criteria (2010 and 1990). All patients underwent clinical evaluation of disease activity and completed the Health Assessment Questionnaire (HAQ), the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), the Dermatology Life Quality Index, and the Leeds Enthesitis Index (LEI). Disease activity was evaluated using the Composite Psoriatic Disease Activity Index (CPDAI), minimal disease activity (MDA), and the Disease Activity Index for Psoriatic Arthritis (DAPSA) scores. Results. The overall prevalence of FM was 17.8% (13 patients), and all but 1 were women (12 patients, 92.3%, p = 0.005). CPDAI and DAPSA scores were significantly higher in patients with coexisting PsA and FM (9.23 +/- 1.92 and 27.53 +/- 19.23, respectively) than in patients with PsA only (4.25 +/- 3.14 and 12.82 +/- 12.71, respectively; p < 0.001 and p = 0.003). None of the patients with FM + PsA met the criteria for MDA, whereas 26 PsA-only patients did (43.3%, p = 0.003). HAQ, BASDAI, and LEI scores were significantly worse in patients with PsA and associated FM. Conclusion. Coexisting FM is related to worse scores on all tested measures in patients with PsA. Its influence should be taken into consideration in the treatment algorithm to avoid unnecessary upgrading of treatment.