This retrospective study was performed to assess the effectiveness of active immunostimulation therapy with bacterial immunotherapy (BIT) in treatment for chronic osteomyelitis (COM). We analyze 154 patients affected by COM and treated with BIT from 1995 to 2009 at our Institution. Using Cierny and Mader classification, patients were divided according to their clinical status and anatomic nature of septic process. The data were analyzed considering several confounding factors, such as antibiotic therapy and hyperbaric oxygen therapy combined with the administration of BIT. According to clinical and radiographic parameters, patients were considered as unchanged, improved, or healed. After a mean follow-up of 40.4 months (median 38 months), healing was achieved in 41.6 % of cases. Multivariate statistical analysis showed that patient’s clinical status is the most important prognostic factor of responding (p < 0.0005) and healing (p = 0.008) after therapy. The best healing rate (62 % of cases) was achieved in patients with a normal clinical condition (Cierny-Mader group A); it was worse (20 % of cases) in those patients with a compromised clinical status (Cierny-Mader group B). There was no healing case in group C. The results show the effectiveness of BIT in treatment of patients affected by COM with uncompromised clinical status. The use of this therapy must be assessed critically in patients with alterations in clinical conditions. Fosco, Gualdrini, Ben Ayad, , , , , , (2014). The role of active immunization therapy as preoperative treatment for chronic osteomyelitis.¬†Musculoskeletal surgery, 2014 Jun;98(1):45-52.¬†https://www.ncbi.nlm.nih.gov/pubmed/23728857