OBJECTIVES: To determine the age of onset of urolithiasis in patients with urinary calcium stones and to establish the relationship between age of onset and clinical profile and metabolic risk factors.METHODS: A total of 500 patients with the diagnosis of calcium urinary lithiasis (average age 47.4 years, range 20-75) were asked regarding the age of onset of the disease. Age of onset of urinary stone disease was compared with other factors such as gender, family history of lithiasis, clinical course, unique or recurrent episodes, and metabolic disturbances found in a comprehensive metabolic evaluation, using the chi-square test for categorical variables and analysis of variance (one way-ANOVA) with the Scheffe test for continuous variables.RESULTS: Mean age of onset of urinary stone disease was 38 years (range 4-73 years). This age of onset was lower in patients with low diuresis (31 years), family history of urolithiasis (32 years), hypercalciuria (36 years), recurrent disease (37 years), and hyperuricosuria (37 years). Significant differences were found in patients who had family history of urolithiasis (32 years) vs. those who did not have (40 years) (p<0.01); patients with recurrent disease (37 years) vs. patients with a unique lithiasic episode (43 years) (p<0.001); patients with hypercalciuria (36 years) vs. those who did not have (39 years) (p<0.05); and also patients with low diuresis (31 years) vs. those with higher diuresis (39 years) (p<0.001).CONCLUSIONS: The average age of onset of urolithiasis is significantly earlier in patients with low fluid intake habits, family history of urolithiasis, hypercalciuria and recurrent stone disease.