A retrospective case cohort series investigated whether obesity increased the risk of psoriatic arthritis (PsA). The database comprised 934 patients (mean age 47.89 years) enrolled in the Utah Psoriasis Initiative from 2002 to 2008. The main outcome measure was a physician diagnosis of PsA from a self-report questionnaire. Body mass index at age 18 was predictive of PsA (odds ratio [OR]: 1.06; P < 0.01) over and above control variables. Other significant variables predictive of PsA included younger age at onset, female gender, highest worse ever body surface area involvement, Koebner phenomenon and nail involvement (ORs: 0.98, 1.45, 1.01, 1.59 and 1.76, respectively). Current BMI and family history of psoriasis were ...