Of 859 consecutive patients with calcium renal stones, 182 had formed only one stone before entering our program. Ninety-three (51.1%) had idiopathic hypercalciuria or hyperuricosuria; 36 (19.8%) others had a systemic disorder producing stones. The remainder, 53 (29.1%) patients, had no metabolic disorder. The frequency of hypercalciuria was lower than among patients with multiple stones. Compared with recurrent stone formers, patients with single stones were older when they passed their stones, suffered higher rates of complication such as surgery, cystoscopy, and urinary tract infection, and had a lower frequency of idiopathic hypercalciuria. During treatment, 11% formed a new stone in an average follow-up period of three years, a relapse rate similar to that of multiple stone formers; however, those patients with single stones who did relapse formed new stones at lower rates than multiple stone formers. Compared with recurrent stone formers, patients with solitary stones were more often treated with diet alone. Since there were no substantial differences between solitary and recurrent stone disease, patients who have formed a single stone should be evaluated and they should be treated no differently from other patients with stone disease.