The syndrome of hyperostosis and hyperphosphataemia (HHS) is very rare. It can mimic bone infections and tumours. A nine-year-old girl presented with pain in her left lower leg. Radiographs showed patchy sclerosis in the tibial diaphysis. Investigations were normal except for hyperphosphataemia. Open biopsy showed chronic inflammation. Bacterial cultures were negative. Four months later, she had pain in the other leg. On evaluation for hyperphosphataemia, there was increased renal reabsorption of phosphates. She responded to analgesics. In patients between six and 16 years of age, HHS must be considered when there is painful diaphyseal swelling of long bones associated with isolated hyperphosphataemia. The painful episodes can recur. Surgical decompression can be considered if conservative treatment methods are ineffective.