OBJECTIVES: Psoriasis, a chronic inflammatory skin condition, can have significant negative impact on individuals afflicted, particularly among those with severe disease. There are multiple physician-reported measures for assessing severity yet the correlation of these is unclear. This study assessed the correlation of the Psoriasis Area and Severity Index (PASI), Body Surface Area (BSA) and the modified Investigator Global Assessment (IGA) scale; all of which assess patient severity. METHODS: An observational study, consisting of a patient survey and chart review was conducted at eight dermatology clinics across Canada. Individuals over the age of 18 years with a physician-confirmed diagnosis of psoriasis were recruited and stratified according to pre-defined PASI score cut-offs, to have even representation of different disease severity levels: PASI≤3 (mild); 3<PASI≤12 (moderate); 12<PASI≤20 (moderate/severe); PASI>20 (severe). Severity was also assessed at the time of the patient survey using the BSA and modified IGA. Correlation between severity measures was assessed using the Spearman rank correlation measure.  RESULTS: A total of 142 patients were included in the study, subdivided into four severity categories (mild: n=40; moderate: n=41; moderate/severe: n=40; severe: n=21). Mean participant age was 45.7 years; the majority were male (68.3%) and were Caucasian (77.5%). All measures were significantly correlated with one another (p ≪0.001). The BSA and PASI were the most closely correlated measures (r=0.91), followed by the PASI and the IGA (r=0.83) and then the BSA and IGA (r=0.77). The PASI was also significantly correlated with the number of body areas where psoriasis is present, as recorded within the BSA (r=61; p≪0.001). CONCLUSIONS: The findings indicate that the PASI, BSA and IGA severity measures closely align in their assessment of psoriasis severity. This enables the comparison of patient samples assessed using different severity measures in the diagnosis of psoriasis and in the assessment of treatment effectiveness in the real world setting.