Introduction. The therapeutic management of hypophosphatemic rickets in adulthood aims to reduce bone pain, the extent of osteomalacia and improve fracture healing and surgical recovery, but clinicians need to stay alert as potential risks can sometimes exceed the benefits of treatment. Case report. We present the case of a 25 year old male patient who was admitted in our department for evaluation presenting severe bone pain. From his medical history we mention that he was diagnosed with rickets at the age of 3 years and received treatment with vitamin D and calcium with no clinical response. A corrective surgery for femur valgus was performed two years later. Because he received high doses of vitamin D without improvement of symptoms the suspicion of vitamin D-resistant rickets was raised at the age of 12 years and treatment with calcitriol 3 tb/day was started with a decline of alkaline phosphatase level from 1144 to 509 UI/l. Two years ago he was diagnosed with renal microlitiasis and left tibial fracture. At present admission he presented with disarmonic short stature, H=149.4 cm (–4.14 SD), W=59 kg, macrocephaly, dental dystrophy and leg bowing. He was under chronic treatment with active vitamin D analog 2 tb/day. Laboratory tests revealed low phosphate (P=2 mg/dl), low 25-OH-vitamin D (19 ng/ml) and 1,25-(OH)2-vitamin D (13.2 pg/ml), normal serum and urinary calcium, normal PTH, high beta crosslaps. In order to diagnose hypophosphatemic rickets, serum FGF23 analysis was performed and it was elevated , but the genetic testing for hypophosphatemic rickets was not available. Because the patient had severe bone pain, a tibial fracture and intented to perform a corrective osteotomy we decided to start medical treatment with elemental phosphorus for 9—12 months, at least 3—6 months before surgery with strict monitoring of serum and urinary calcium and phosphate level, creatinine, alkaline phosphatase and serum PTH. Conclusion. The key point of the case is the late diagnosis of hypophosphatemic rickets and the challenge in treating our patient in order to minimize the risks of combined treatment with calcitriol and phosphorus giving the fact that he was already diagnosed with nephromicrolitiasis.