Indirect treatment comparisons are used when no direct comparison is available. Comparison networks should satisfy the transitivity assumption, that is, equal likelihood of treatment assignment for a given patient based on comparability of studies. Seven criteria were evaluated across 18 randomized controlled trials in psoriatic arthritis: inclusion/exclusion criteria, clinical trial design and follow-up, patient-level baseline characteristics, disease severity, prior therapies, concomitant and extended-trial treatment and placebo response differences. Across studies, placebo was a common comparator, and key efficacy end points were reported. Collectively, several potential sources of insufficient transitivity were identified, most often related to trial design and population differences. Potential challenges in satisfying transitivity occur frequently and should be evaluated thoroughly.