Objective: In clinical studies, it is crucial to assess psoriasis severity accurately and with no substantial variation between different raters. The Psoriasis Area and Severity Index (PASI) and Physician Global Assessment (PGA) are the two most commonly used tools for the assessment of psoriasis severity. The aim of this study was to evaluate the intra-rater and inter-rater reliability of these methods and to determine whether inter-rater reliability is affected by rater experience. Design: An open uncontrolled study Setting: Dermatology Department of Ege University, Medical Faculty Subjects: Fifty-five patients with plaque psoriasis who were examined between 15 August 2012 and 15 November 2012 in the dermatology department of Ege University Interventions: Three dermatology residents with varying experience evaluated the patients individually using both the PASI and PGA for each patient (in that order). Main Outcome Measure: PASI and PGA Results: PASI and PGA scores showed high intra-rater correlation for all three residents. Inter-rater reliability for PASI was high between the most experienced and second most experienced resident and between the most experienced and least experienced resident. However, inter-rater reliability for PGA was high between the most experienced and second most experienced residents, but only moderate between the most experienced and least experienced resident. Conclusions: There were no significant interrater differences between PGA and PASI scores in our study. However, because PGA is more subjective and may be affected by rater experience, PASI is considered to be a more reliable method for assessing severity of psoriasis. © 2021, Kuwait Medical Association. All rights reserved.