OBJECTIVE We aimed to carry out a systematic assessment of gray-scale and color Doppler ultrasonography (CDUS) findings of reactivated post-traumatic/postoperative chronic osteomyelitis (COM) in adults. METHODS Gray-scale and color Doppler ultrasonography were performed on 40 consecutive patients with a history of long-standing post-traumatic/post-operative chronic osteomyelitis and clinical suggestion of reactivation, in a 32-month-period. All patients had metallic implants: 16 internal fixations, nine external fixations, 11 hip arthroplasties and four knee arthroplasties. The final diagnosis of reactivated COM was based upon biopsy findings, with microbiological and histological examination (n = 27), or a combination of laboratory, clinical and magnetic resonance (MR) findings (n = 13). The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of sonographic signs, including fistulous tracts, periosteal thickening, cortical discontinuity, soft tissue abscess and cellulitis, juxtacortical fluid, distension of the pseudocapsule in arthroplasties, and periosteal vascularity, were estimated. RESULTS Statistically significant differences between patients with and without reactivated COM were found for fistulous tracts (P < 0.0001), juxtacortical fluid collections (P < 0.001) periosteal thickening (P < 0.01), distension of pseudocapsule (P < 0.05), and periosteal vascularity (P < 0.0001). Low-resistance arterial flow of periosteal vessels presented the highest sensitivity (92%), specificity, and PPV (100%), yielding only two false negative results in two obese patients. Among gray-scale findings, the presence of a fistulous tract yielded the highest specificity and PPV (100%), whereas periosteal thickening was the most sensitive (92%), though not specific, finding (specificity 50%). CONCLUSIONS A constellation of gray-scale and CDUS findings can be highly indicative of reactivated bone infection in patients with long-standing chronic post-traumatic/post-operative osteomyelitis.