OBJECTIVES: To assess the comparability of the trials included in network meta-analyses (NMAs) comparing biologic treatments in moderate to severe plaque psoriasis (PsO). METHODS: A systematic literature review identified two recently published NMAs. The definition of ‘moderate to severe’ psoriasis adopted by one of the NMAs was “having an inadequate response to topical treatments alone and either having received prior systemic therapy or being candidate for such therapy”. The second NMA did not report the definition used; instead, the eligibility criteria were defined in terms of the treatments assessed in the randomized controlled trials (RCTs). The eligibility criteria adopted in each RCT and the resulting patient population characteristics were collected in order to assess comparability among the trials in each NMA. RESULTS: The RCTs selected in each of the NMAs adopted diverse eligibility criteria based on body surface area (BSA), psoriasis area and severity index (PASI) score and exposure or failure to previous therapies. Although many of the trials adopted eligibility criteria that aligned with  clinical guideline definitions of moderate to severe PsO as BSA above 10% and PASI above 10, the resulting ‘moderate to severe’  populations showed wide variation in their baseline characteristics. Analogous differences in placebo responses were observed. For example, baseline PASI scores ranged from 14 to 23, while the proportion of patients with a 75% reduction in the PASI scores at 12 weeks varied from 2% to 18% among the trials in each NMA. CONCLUSIONS: The current definitions of ‘moderate to severe’ PsO do not seem enough to guarantee similarity in severity across trials, which may lead to imbalance in the distribution of potential effect modifiers across comparisons, and consequent bias in the NMA estimates. In the absence of better characterization of the patient population, adjusting for baseline risk is advisable.