Background and aims   The most common identifiable causes for ILD are related to occupational  and environmental exposures, especially to inorganic dusts and silica dust in one of the most   important occupational respiratory toxins that causes silicosis. Silicosis can occur in chronic,  accelerated and acute forms. Occupational exposure to crystalline silica dust in many industrial  operations world wide. The reduction of silica dust exposure level in most developed countries   during the last century resulted in dramatic decreases in morbidity and mortality from silicosis  and silica dust associated tuberculosis but exposure risks can be much greater in underdeveloped  countries. Silicosis is disabling, non eversible and sometimes fatal. We believe same of this reports is very rare in the world wide and demonstrate the first fatal outbreak report of advanced   silicosis in Iran.   Methods   All of 17 workers had been exposed to crystalline silica at the workplaces of silica  powder production for the periods of 1 to 5 years (the average of exposure was 2.7 years) and  because dyspnea and occupational history of silica dust exposure referred or self admitted at  Urmia occupational medicine centre. All patients reported no silica exposure before working at the current sites. Compliant symptoms and physical examination findings recorded for each patient. Spirometery.Flow/volume and body plethysmography performed (with a ZAN.300).  chest X-ray films were taken for catch person and in those, who had previous chest X radiography  films, progression was assessed by pair comparison of the initial and latest chest X-ray film according to ILO classification of pneumoconiosis   Results   All of 17 patient had previously worked in the silica powder production workplaces. The total of patient were male whose youngest age was 20 and oldest 79 years. 16 (94%) cases were  symptomatic and 1 (6%) had any complaint but occupational history and radiographic findings  suggest sub clinical accelerated silicosis. most common findings during clinical course weredry cough 15(88%) productive cough 5 (29 %) ,anorexia 11 (65%), weight loss 11 (65%) orthopnea 10 (58%), respiratory distress 9 (53%), dysphagia 5 (30%), fibromyalgia 6(35%), small joints  arthragia 1 (6%), rude crackle 14(82%), decreased of pulmonary expansibility 15 (88%),  symmetric PIP arthritis 1 (6%), symmetric wrist joints arthritis 1 (6%), and anemia 1 (6%),  11(65%) patients had FVC lower than 50% of predictive measured. 17 (100%) cases had small  opacity. Large opacity were find in 14 (82%) , pleural thickening 12 (71%). 9 (52%) patient during  last 5 years died due to ARDS   Conclusion   The findings in this outbreak shows that from 17 patient ,15 (88%) subjects were  young adults below 40 years old and dying 9 (53%) persons after 1 to 5 years exposure incision to  silica dust suggests overexposure had occurred and led the development of advanced silicosis. This outbreak illustrate the very rare manifestations of chest imaging of severe silicosis in the world wide.