OBJECTIVE: To estimate the prevalence of psoriatic arthritis (PsA) in primary care patients diagnosed as having psoriasis and to estimate the prevalence of musculoskeletal symptoms in psoriasis patients in primary care. METHODS: We conducted a cross-sectional study in adult primary care patients with psoriasis. Responding patients reporting pain in joints, entheses, or the lower back were interviewed by telephone to determine eligibility and, if eligible, were invited for clinical evaluation. During clinical evaluation, skin, nails, joints, and entheses were assessed. Additionally, ultrasound of the enthesis was performed by an independent trained examiner if a patient had at least 1 tender enthesis (determined by the Leeds Enthesitis Index and the Maastricht Ankylosing Spondylitis Enthesitis Score). Patients who fulfilled the Classification of Psoriatic Arthritis (CASPAR) Study Group criteria were classified as having PsA. RESULTS: We invited 2,564 psoriasis patients from databases of 97 participating general practitioners. Of 1,673 responders (65.2%), 841 (50.3%) were willing to participate. A total of 823 patients (32.1%) reported having musculoskeletal symptoms; 659 of these patients were determined to be eligible, 524 of whom were clinically evaluated. We identified 64 cases of established PsA and another 17 cases of newly diagnosed PsA, leading to a prevalence of 3.2% (95% confidence interval [95% CI] 2.5-3.9) among psoriasis patients in primary care. This prevalence would increase to 4.6% (95% CI 3.8-5.4) if PsA cases based on enthesitis were also taken into account. CONCLUSION: Among psoriasis patients in primary care, the prevalence of PsA is conservatively estimated to be 3.2%, increasing to 4.6% if enthesitis is taken into account. The prevalence of musculoskeletal symptoms among psoriasis patients is comparable with the prevalence of musculoskeletal symptoms in the general population.