Intermediate-term immobilization may lead to an increase in serum and urinary calcium. In order to test this hypothesis, we evaluated 46 children, 21 with Legg-Calvé-Perthes disease (LCP; 7.2±1.8 years old) and 25 with developmental dysplasia of the hip joint (DDH; 10±5 months of age), submitted to immobilization for up to 16 weeks. These two conditions require intermediate-term immobilization as treatment modality, and no studies evaluating calcium metabolism in these groups of patients have been conducted. In LCP patients, blood and 24-h urine samples were obtained before the beginning of treatment and after 1, 6, 8, 14 and 16 weeks of immobilization, while in DDH patients, blood and spot urine samples were collected before treatment and after 6 and 14 weeks of treatment. Urinary calcium, creatinine, potassium and sodium as well as serum calcium, phosphorus, parathyroid hormone, creatinine and alkaline phosphatase were determined in those samples. Renal ultrasound was performed before and after treatment. A mean increase of 2.3 times baseline values of urinary calcium was observed in 40% of previously normocalciuric LCP patients after only 1 week of immobilization. Among the DDH children, who had never previously ambulated, there was no significant variation in the urinary calcium excretion. None of the serum parameters changed in either group throughout the study. Urinary stones were not evidenced by renal ultrasound. Therefore, the present data suggested that intermediate-term immobilization led to a transient increase in urinary calcium in 40% of LCP patients. Complications such as urinary stones were not observed. In conclusion, this modality of treatment does not impose an increased risk of urinary stone formation in LCP and DDH patients.