OBJECTIVES: The Psoriasis Index of Quality of Life (PSORIQoL) is a 25-item quality of life (QoL) scale specific to psoriasis. It has been shown to have excellent scaling properties and to be reproducible and valid. The aim of the present study was to assess the responsiveness of the PSORIQoL and provide data that will aid in the interpretation of scores on the measure. METHODS: Data from a 13-week, placebo-controlled clinical trial in psoriasis were analysed. PSORIQoL responsiveness was assessed using Effect Size (ES), Standardised Response Mean (SRM) and the Responsiveness Statistic (RS). The Standard Error of Measurement (SEM), a distribution-based method of interpreting scores was also calculated. An anchor-based Minimal Important Difference (MID; which provides an assessment of clinical meaningfulness) was derived by measuring QoL change accompanying changes in disease severity on a six-point Investigator’s Global Assessment (IGA). The IGA ranges from zero (clear) to five (very severe disease). RESULTS: A total of 69 psoriasis patients completed the PSORIQoL (51/ 74% male; mean age 43.8 +/-11.7; baseline mean PSORIQoL = 12.2 +/- 6.4; 13-week PSORIQoL = 9.8 +/- 7.1). Effect Sizes ranged from 0.37 for the placebo arm to 0.67 for the most potent treatment arm. Changes for the whole sample were significant over time (p=.007), with SRM = 0.40 and RS = 0.51. According to ES, changes of 1.3, 3.2, and 5.1 represent small, moderate and large changes in PSORIQoL scores respectively. One SEM = 1.91; 1.96 SEM = 3.75. A move from Severe to Moderate and from Moderate to Mild disease on the IGA requires a change of 1.8 and 2.7 points, respectively in PSORIQoL scores. CONCLUSIONS: The PSORIQoL was shown to be responsive to treatment effects. The MID for the measure is between two and three points.