Psoriasis treatment is highly individualized. Although a standardized assessment of psoriasis severity for clinical practice may be theoretically advantageous for the purposes of determining treatment, the relevance of currently available research tools in clinical practice is uncertain. Our objectives were to ascertain in workshop discussions and through a prospective survey the relevance of standard severity measures in clinical practice with regard to choice of treatment. Although there was agreement on the possible structure of an algorithm for the treatment-related definition of psoriasis severity, consensus on the cut-off levels for the PASI and %BSA that would indicate a switch in treatment mode could not be reached. The lack of agreement prompted a prospective survey of 112 patients with psoriasis from 10 countries. This survey used a formal questionnaire asking for the PASI and %BSA scores, the patient's self assessment score (VAS ranging from 0 to 10), location of the psoriatic lesions and disease phase. Severity scores from 20 patients pre-selected for inclusion in a trial of a biological agent were included for comparison. Severity scores were analysed in relation to the choice of treatment (topical or systemic, which included phototherapy and combination) suggested by the treating physician.PASI scores differed significantly between the treatment groups (topical vs systemic, p=0.009); however, there was large overlap in the range of PASI scores between the groups. The same was true for VAS scores (topical vs systemic, p=0.035). %BSA scores were not significantly different between treatment groups. There was a large overlap for both the topical and systemic treatment groups with the biologicals group for the range of both the PASI and %BSA scores. A standardized protocol for the evaluation of psoriasis severity based on established severity scores (PASI, %BSA) appears to be unrealistic in day-to-day clinical practice. In clinical practice, a host of factors must be evaluated alongside possible metric measures. This requires experience and the specialized medical education of those involved in the treatment of patients with psoriasis.