Objective: to investigate prevalence of some scaly and erythematosus skin diseases at the National Hospital of Dermatology and Venereobgy (NHDV). Method: case series study based on retrospective data of all patients diagnosed as psoriasis, parapsoriasis, pityriasis rosea at NHDV from 1/1/2009 to 31/12/2011. Results: The prevalence of scaly and erythematosus skin diseases was 2.87 percent of all skin diseases. Male/female ratio was 1.5. The diseases were seen more frequently in patient:, aged 15-44 years, accounted for 64.5 percent, in self-en ,ployed group 44.7 percent, students 21.5 percent. Of the total r atient visits at NHDV, psoriasis was 2.16 percent
parapsoria~is 0.13 percent and pityriasis rosea 0.59 percent. Psoriasis was seen commonly in the age group of 25-34 years ( 20 percent) and increased in spring and winter, redu. oed in the summer, autumn. Pityriasis rosea was frequently seen in the group of 15-34 years (75 percent), increased in the fall. Parapsoriasis was more common in the age-group of 15-34 years ( 50 percent), and the trend was stable over the months. Conclusion: The scaly red skin diseases were relatively common among the skin diseases, commonly seen in adults and changed as the seasons.