Dietary and drinking habits of 277 male renal stone patients and the same number of their coworkers, who served as age- and sex-matched controls, were investigated to clarify the effects of dietary habit on stone formation. The results were compared with those for 4, 386 age-matched healthy male Japanese. We found that the stone formers had dietary habits underirable for prevention of stone formation. On the other hand, their co-workers also had more unbalanced dietary habits than the healthy Japanese, and their dietary habits were intermediate between those of the stone formers and the healthy subjects. This investigation revealed that the socio-economic conditions of both the stone formers and their co-workers may play some part in stone formation, and that their co-workers who are in a social situation similar to that of the stone formers may themselves become stone formers eventually if they continue their poor dietary habits such as unbalanced diet and over-eating. It is speculated that greater public awareness of the importance of diet habits is necessary for reducing the risk of renal stone formation.