To disclose the risk factors for immunoglobulin A nephropathy (IgAN), we conducted a case-control study in the Tokai area of central Japan. The subjects were 94 patients, aged 20 years or older at diagnosis, who had histologically confirmed IgAN. Two sex-, age-, and residence-matched controls were randomly selected for each case from the general population. Information on medical history and lifestyle was collected using a self-administered questionnaire. The strength of association between IgAN and a potential risk factor was assessed by calculating an odds ratio. A family history of chronic nephritis, susceptibility to the common cold, preference for salty foods, frequent consumption of raw eggs, and a high intake of carbohydrates, including rice, were significantly associated with an increased risk for IgAN. Alcohol consumption, use of antioxidant vitamin supplements, and a high intake of protein, fat, monounsaturated fatty acids, and all/n-3 polyunsaturated fatty acids were somewhat protective against IgAN. Episodes of tonsillitis and exposure to organic solvents were found not to be associated with the risk in the present study. Our findings may provide some clues to the cause of IgAN.