The epidemiological literature on the health effects of occupational exposures in the leather and leather products industry (SIC-5199) is reviewed, and epidemiological methodology is explained. The increased incidence of bladder cancer among workers in the leather industry is noted along with excess mortality rates from mouth, laryngeal, pharyngeal, and nasal cancer. Hazardous chemicals to which leather workers are exposed, such as the chromates and benzidine based azo dyes, are described. The methodology of retrospective epidemiological studies to determine the long term health effects of industrial exposure is discussed, and the establishment of recordkeeping procedures and research designs for prospective epidemiological studies is delineated. The author concludes that epidemiology is an invaluable research tool for detecting the chronic effects of occupational exposure to hazardous substances.