Fifty-Four patients completed a questionnaire to assess functional lifestyle disability caused by psoriasis and a detailed record of the area of psoriasis involvement was taken. The 10 most relevant and independent questions were identified from the original 28 questions and the final questionnaire score, the Psoriasis Disability Index (PDI), was used to quantify reduction in disability before (34. 1±11. 1) and after (22. 3± 10. 9, n=20, P<0. 002) in-patient treatment. The total area of involvement of psoriasis is not a reliable guide to disability. The PDI may be used as a repeatable measure and record of disability caused by psoriasis and may potentially aid psoriasis management decision taking.