In order to evaluate the recurrence of calcium kidney stones, 520 patients (275 males and 245 females), aged 14-79 years, previously treated with lithotripsy were followed up for 23 months on average (median = 24 months; range = 12-48 months), and 101 relapses (10%/year) were recorded. Among the possible predictors of recurrence, measured at the beginning of the follow-up and analyzed in univariate and multivariate statistical ways, age was inversely related with occurrence of event (multivariate t value = -2.12) whereas urinary calcium (UC; t = 2.78), alkaline phosphatase (AP; t = 3.55) and history of previous relapses (t = 2.07) were directly related to the recurrence. The levels of UC were not correlated to those of AP (linear correlation coefficient r = 0.0032), but the combination of their high levels increased the risk of recurrences. The contribution of the other considered factors to stone formation were not significant (sex, family history of stone disease, gallstone, renal failure, serum calcium, phosphate, uric acid, sodium and proteins, urinary phosphate, sodium, magnesium and uric acid.