Abstract: AIM: The aim of this study was to assess the demography of Polymyositis in Iran. Methods: In the past 20 years, we had seen 124 patients in Rheumatology Research Center. All patients were classified by the American College of Rheumatology classification criteria. Ninety five items were checked for every patient. All patients were followed regularly and the data were updated at each visit. Results: Seventy one patients were female. The female to male ratio was 2. The acute presentation of the disease was seen in 10%. The manifestations at the onset of disease were fever in 16%, muscle weakness 45%, myalgia 21%, arthralgia 38%, specific rash 25%. The clinical manifestations during the disease were: Fever 52%, weight loss 44%, fatigue 50.8%, proximal weakness 98%, myalgia 44%, muscular edema 16%. eyelids edema 33%, heliotrope erythema 41.9%, articular rash 35.5%, periungual erythema 9.7%, malar rash 25.8%, hair lass 39.8% , Calcinosis 5.6%. arthralgia 56%, arthntis 56%, joint deformities 10% , cardiac manifestations 11%, Ravnaud's phenomenon 20%, pulmonary involvement 24%, and dysphagia in 39% of cases. Lab tests: increased muscle enzyme in 99% of cases, myogenic pattern in electromyography in 95% of cases, and myositis pattern of the muscle biopsy in 93% of cases. Conclusion: 1- Polymyositis features in Iran were the same as in other countries. 2- The most common presentation was the insidious form. 3-The most common manifestation was the muscle weakness. 4- Osteoarticular involvement was not rare in Iranian patient.