Kidney stones can form during a state of urinary supersaturation. Because urine often is supersaturated with respect to various salts, crystal formation is very common in nonstone formers and stone formers alike, and it may even be absent in kidney stone formers. Thus, uncomplicated crystalluria does not distinguish between stone formers and healthy people. Landmark clinical studies, however, have shown that under identical conditions of dietary and fluid intake, healthy controls almost exclusively excrete single calcium oxalate crystals 3 to 4 microns in diameter, whereas recurrent calcium stone formers pass larger crystals, 10 to 12 microns in diameter, often fused into polycrystalline aggregates 20 to 300 microns in diameter. Thus, those who form stones appear to be more "sensitive" to a given diet than nonstone formers. It is in these subjects that "bad dietary habits" induce nephrolithiasis, making nutritional aspects important. This article reviews the current evidence-based knowledge of the impact of nutrition on the recurrence of a kidney stone.