The aim of this study was to compare Tc-99m nanocolloid scintigraphy with Tc-99m MDP bone imaging in the diagnosis of osteomyelitis and septic arthritis. Overall, 31 Tc-99m MDP bone scans and 39 Tc-99m nanocolloid studies were performed in 34 patients (15 female, 19 male; mean age, 14.88 years +/- 19.00 years) who were suspected of osteomyelitis and/or septic arthritis. The final diagnoses were established by needle aspiration, cultures, radiography, clinical course, and, in some patients, with CT, ultrasonography, and biopsy. The sensitivity, specificity, and accuracy were 100%, 75%, and 92%, respectively for both Tc-99m MDP and Tc-99m nanocolloid scans in detecting osteomyelitis. For septic arthritis, Tc-99m MDP bone imaging showed 100%, 85%, and 94%, and Tc-99m nanocolloid scans showed 90%, 59%, and 76%, sensitivity, specificity, and accuracy, respectively. These results show that, although both scans are in good agreement for osteomyelitis, for septic arthritis nanocolloid is not specific enough to recommend it to be a complementary method to MDP bone scans.