Objective: To assess the severity of psoriasis over time. Design: We analyzed the results of structured dermatologic examinations administered over a 20-year period beginning 10 years after study enrollment. Setting: The PUVA [psoralen-UV-A] Follow-up Study, which is a prospective cohort study. Patients: The analyses were restricted to 815 patients (83.2% of those eligible) who underwent at least 2 of 4 possible examinations between 1985 and 2005. Main Outcome Measure: A 4-point physician global assessment (PGA). Results: The distribution of the PGA levels in the study group did not change significantly over time, except that in 2005 more patients had no psoriasis compared with patients who underwent examinations in the previous study years (9.6% vs <5.1%, P<.03). The PGA level changed more than 1 level between examinations in only 14% of patients. Multistate Markov models estimated that patients had a likelihood of about 80% to remain at the same PGA level 1 year later. After 10 years, this likelihood varied between 19% and 53%, depending on the PGA level. Except for patients who were clear of disease at baseline, on average patients had about 1 year without psoriasis over 20 years. On average, individuals with moderate to severe disease remained at these levels for 11 or more years. Conclusion: Three decades after a large and diverse group of patients sought a cure for their psoriasis, consistent control of their psoriasis often had not been achieved.