We conducted a retrospective study of the course of recurrent urolithiasis in 127 patients (63 women, 64 men aged from 27 to 58) who were under close and regular outpatient follow-up for up to 15 years and who did not receive conservative prophylactic therapy due to different reasons. The group consisted of 33 patients with uric acid lithiasis, 52 patients with calcium oxalate lithiasis, 42 patients with magnesium-ammonium-phosphate lithiasis. By the start of follow-up not a single patient had had urinary stones detected by ultrasound and X-ray. For the period of observation there were up to 7 recurrences diagnosed in each patient and we studied the chemical composition not only of the primary stones but also of 352 recurrent stones by means of infrared spectrophotometry and X-ray diffraction. In our investigation we also performed biochemical and microbiological analysis and urinalysis. We established the chance and we found prognostic factors of changes in the type of stone formation in patients with different chemical forms of the disease. In patients with uric acid lithiasis recurrent stones can be composed of calcium-oxalate or phosphate, in patients with calcium-oxalate lithiasis recurrent stones could be composed of phosphate, and patients with magnesium-ammonium-phosphate stones may develop stones of uric acid or calcium-oxalate.