Objective To characterize the natural history of psoriasis vulgaris.Methods A retrospective study was carried out.Totally,245 patients admitted to hospitals within three months after the first episode of psoriasis vulgaris were selected from 1136 patients with psoriasis vulgaris who had been followed up for more than 20 years.Changes in disease severity during the long-term follow-up were traced,and information on the shape and distribution of skin lesions,family history,use of anticancer drugs,vitamins and traditional Chinese medicines was collected and analyzed.SPSS13.0 software package was utilized to assess factors associated with the evolution of psoriasis vulgaris.Results The natural course of psoriasis vulgaris could be classified into six types:immediate healing,slow healing,intermittent relapse,frequent mild relapse,frequent moderate relapse,and frequent severe relapse.The immediate healing type and slow healing type amounted to 30％ of these patients,and the frequent severe relapse type to less than 10％.Statistical analysis revealed that the clinical severity of psoriasis was associated with the age of onset and family history,and was negatively correlated with the use of anticancer drugs.Conclusions The long-term follow-up study reveals the natural course of psoriasis vulgaris,which may be helpful in guiding the prediction of prognosis,prevention of recurrence and selection of treatment.