Aim: 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. Materials & methods: 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. Results: 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. Conclusion: Potential challenges in satisfying transitivity occur frequently and should be evaluated thoroughly.