A study of the prevalence of silicosis was conducted for a cohort of 190 workers in a Thai refractory brick factory (SIC-3255). Workers completed a questionnaire to obtain information on demographic characteristics, occupational history, smoking habits, and respiratory history and were given physical examinations that included pulmonary function testing and chest X-rays. Eighteen cases of silicosis were identified, yielding a prevalence rate of 9.5%. The mean age of the cases was 49.6 years and mean years of exposure was 23.9 years. By sex, the silicosis prevalence rates were males 7.6% and females 27.1%. When stratified by job description, the prevalence rates for workers preparing raw material, green brick production workers, and workers involved in repairing brick molds were 15.7, 12.8, and 10%, respectively. Seven silicotic subjects complained of weakness, dyspnea, low grade fever, and chest pain; with two demonstrating finger clubbing and cyanosis. Approximately 44.4% of the silicotic subjects had abnormal pulmonary function indicative of a restrictive ventilatory defect. Two cases of silicotuberculosis were detected. A nested case control study was conducted and revealed that persons who had been employed at the facility for 25 years or longer had a risk of developing silicosis 20.8 times that of those who had worked for shorter periods. Smoking was not a risk factor for silicosis. The authors conclude that the prevalence of silicosis among the work force is rather high. Local exhaust ventilation and other engineering controls should be applied to protect the health of the workers who have not yet developed silicosis. Workers with clinically confirmed silicosis who are under 50 years old should be removed from exposure and followed up annually.