OBJECTIVES Psoriatic arthritis (PsA) is a multi-factorial disease that affects the skin, joints and soft tissues. Two of the commonly used measures for PsA are the Psoriasis Area and Severity Index (PASI, 0-100 scale) and the Health Assessment Questionnaire (HAQ, 0-3 scale) for skin and joints symptoms, respectively. Previous work in the area has estimated a relationship between these patient-reported instruments and utility (SF-36 mapped to the EQ-5D). The objectives of this study were to calculate patient-reported utility and investigate the consistency of the relationship between PASI, HAQ and utility with previously published estimates, based on the PSUMMIT trials of ustekinumab versus placebo. METHODS Patient level data from PSUMMIT1 (anti-TNFα naïve) and PSUMMIT2 (both anti-TNFα naïve and experienced) were analysed in Stata 11. SF-36 data were converted to EQ-5D using the mapping by Rowen et al., with regression analysis used to estimate the relationship between PASI, HAQ and the resulting utility (including multiplicative terms). Goodness of fit was determined by the adjusted R and Root Mean Squared Error (RMSE). RESULTS Anti-TNFα naïve and experienced patients had a baseline utility of 0.50 and 0.48, respectively. Utility improved over the 24-week blinded period by 0.04/0.06 in the placebo arms for anti-TNFα naïve and experienced, and 0.11/0.13 in the treatment arms. In regression analysis utility was predicted as 0.897 – 0.004xPASI - 0.298xHAQ (adjusted RCONCLUSIONS Patients with PsA have a low level of health-related quality of life that improves with treatment. The determinants of utility in the PSUMMIT trials were the skin and joint symptoms faced by patients, in keeping with previous estimates.