Osteologic practice occasionally includes problems of diagnosis and therapy of bone tumours. Clinical signs common to many bone disorders are also present in patients with primary bone tumours: swelling, tenderness, pain on motion, stiffness and pathologic fractures. The most prominent constitutional symptoms are loss of weight, anorexia and fever. Primary bone tumors are rare (about 1% of all malignancies), deceptive in their presentation, clinical and radiologic features are often non-specific and histologic pictures of malignant neoplasms can be easily confused with benign conditions. Therefore, the aim of this chapter is to raise awareness of these diagnostic problems so that the diagnosis is made early and effective therapy can be started. It is also important to emphasize that patients with possible malignant bone tumours are referred to centres familiar with these neoplasms, including osteologists, oncologists, surgeons, radiologists and histopathologists. Only by the cooperation of these specialists can mistakes in diagnosis be avoided and early treatment can be started without delay.