Hyperbaric oxygen therapy is considered a non-invasive therapeutic tool with proven efficacy in the treatment of various bone diseases in adults and children, in addition to or as an alternative to conventional therapy. Its use in patients with chronic osteomyelitis is recommended in guidelines and can lead to a marked improvement in the clinical picture and images. The paper reports the clinical case of a 9-month-old child with acute osteomyelitis that was clinically cured and without persistence of inflammation indices, but with the persistence of an unfavourable evolutionary picture on MRI. A cycle of hyperbaric oxygen therapy produced an evident and rapid improvement in the observed picture. Hyperbaric oxygen therapy should also be considered in the presence of an evolution of acute osteomyelitis which, despite the absence of clinical and laboratory criteria to formalize the diagnosis of chronic osteomyelitis, shows a not favourable evolution in terms of reparative phenomena on MRI performed after a reasonable distance of time.