Silicosis is the disease most associated with crystalline silica exposure; it is incurable but preventable. This debilitating and often fatal lung disease persists worldwide despite long-standing knowledge of its cause and methods for controlling it. This Hazard Review, Health Effects of Occupational Exposure to Respirable Crystalline Silica, describes published studies and literature on the health effects of occupational exposure to respirable crystalline silica among workers in the United States and many other countries. The review indicates a significant risk of chronic silicosis for workers exposed to respirable crystalline silica over a working lifetime at the current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL), the Mine Safety and Health Administration (MSHA) PEL, or the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL). In addition to the risk of silicosis, epidemiologic studies indicate that workers exposed to respirable crystalline silica have an increased risk of developing lung cancer, pulmonary tuberculosis, and airways diseases. The latest scientific information also indicates possible associations of occupational exposure to silica dust with various other adverse health effects.