Introduction: The problems of the differential diagnosis (d.d.) between musculoskeletal infections and tumours are generally uncommon because both pathologies are quite rare. This is not the experience at the G. Pini Orthopaedic Institute where there are two Units specialized on bone infections and bone tumours and their clinicians often consult each other for difficult cases.

Material and Methods: On the basis of this experience, the A.A. revised clinical and radiological criteria of d.d. between acute or chronic osteomyelitis and different histotypes of musculoskeletal tumours. In particular they examined the type and the course of the symptoms, the laboratory data, the site of the lesions and the characteristics of the imaging, both for bone damages and for soft tissues invasion. Afterwards they compared this revision whit the experience of the cases consulted each other.

Results: D.d. of acute osteomyelitis include Ewing sarcoma, Osteosarcoma and Eosinofilìe granuloma, especially in children; d.d. of chronic and deep lesions (axial skeleton) in adults include lymphoma and metastasis; in the epiphysis d.d. can involve also benign lesions. This work allowed the A.A. to identify some guidelines that they consider suitable. Time, possibilities and limits of the imaging techniques like bone scans, CT and MRI are outlined, likewise time and types of direct examination of the lesions by puncture or biopsy, that was necessary in many cases, are proposed.

Conclusions: The A.A. think that these personal guidelines can help them to face easier, in the future, the difficult cases, minimizing both diagnostics and therapeutics delays and mistakes.