The clinical manifestation of oncogenic osteomalacia includes bone pain, pathological fractures, general fatigue and muscle weakness. Such unspecific symptoms hinder the establishment of a proper diagnosis which very often requires long-lasting investigations with many diagnostic imaging methods. Here, we discuss difficulties in the diagnosis of oncogenic osteomalacia using the example of our own clinical case: a 56 year-old woman with a history of pain in the left hip and two years of walking difficulties. A plain radiograph and CT scan revealed pathological fractures. Multiple myeloma, primary hyperparathyroidism and bone metastatic disease were excluded. Routine laboratory tests showed elevated alkaline phosphatase and a mild degree of hypophosphatemia. CT and MR imaging confirmed the presence of a pathological mass in the thorax. Tumour excision and histopathological test results revealed the diagnosis of a phosphaturic mesenchymal tumour. Our case, showing the clinical course of the disease from the symptoms manifested at the beginning to the establishment of the diagnosis, can serve as a model illustration of the diagnostic struggle involved with oncogenic osteomalacia.