A 12-year-old patient with a severe traumatic brain injury developed heterotopic ossification (HO) with rapidly decreasing range of motion in multiple joints despite intensive passive range of motion exercises and the use of nonsteroidal antiinflammatory drugs (NSAIDs). His alkaline phosphatase was markedly elevated. Etidronate, 20mg/kg/d was used to control the ossification. After 7 months of continual etidronate use, the patient developed periarticular pain with widened growth plates, suggesting a rachitic syndrome. Serum laboratory panel including calcium, phosphorous, alkaline phosphatase, and vitamin D were normal. After 3 months off etidronate, radiological studies showed growth plate calcification, though not before development of bilateral slipped femoral capital epiphyses. Further improvement and resolution of all complications occurred 5 months after discontinuation of etidronate. Rachitic syndromes secondary to didronel use in a clinical setting has not been previously reported. Other possible causes for a rachitic syndromes were not present. Alternate treatments for children with or at risk for HO should be considered.