The administration of ceftriaxone is known to be associated with biliary pseudolithiasis, although the development of urolithiasis has only rarely been reported. We treated a young male with bacterial meningitis complicated by urinary precipitates composed of ceftriaxone-calcium salt, which prompted us to study whether ceftriaxone administration predisposes children to the formation of urinary precipitates. The case-control study reported here included 83 children with bacterial pneumonia aged from 3 months to 8.9 years. The children were divided into one group of 43 children who received ceftriaxone (group A) and a second group of 40 children who received amoxicillin (group B). Paired samples of serum and urine before and after treatment were obtained from the patients in each group. There were no significant differences in demographic characteristics and blood biochemistry between the groups. However, the mean urinary calcium to creatinine ratio (uCa/Cr; mg/mg) was significantly higher in group A patients than in group B patients after treatment (0.19 vs. 0.09, respectively; p < 0.001), and analysis of the paired urine samples revealed that the uCa/Cr significantly increased after treatment only in group A patients(p < 0.001). There was a weak but non-significant relationship between the dose of ceftriaxone and the uCa/Cr in group A (p = 0.10, r = 0.24). Our results are the first to demonstrate that ceftriaxone has the potential to significantly increase urinary excretion of calcium, which may be linked to ceftriaxone-related urolithiasis or sludge. We therefore suggest that it is worthwhile monitoring the uCa/Cr levels in patients on ceftriaxone as they may be at greater risk for developing large stones and renal damage.