Objectives:  The aim of this series of cases was to evaluate the differences and reactions of tissues around immediate implants placed in infected or noninfected sockets in mandibular molars, with or without bone graft placement. Methods: Four immediate implants were placed in infected or non-infected mandibular molar sockets in four patients. The patients were divided into 2 groups (n=2). In Group 1 a bone graft was placed and in Group 2 no bone graft was placed. Clinical and radiographic evaluations were performed 8 days and 4 months after implant placement in all patients. Results: At 4 months follow-up, both groups showed favorable bone-implant integration, and the survival rate of both groups was 100%. No greater difference was observed between the 2 groups to the radiographic evaluation at 8 days and 4 months related to changes in the level of the bone crest in the vertical and horizontal direction. No major differences were found in bone and soft tissue regeneration between cases where bone graft was placed, and in the cases where bone grafting was not used. Conclusions: Within the limitations of this study, we can conclude that immediate implant placement in infected or noninfected sockets in mandibular molars, with bone graft or without grafting does not present differences.Objetivos: Evaluar las diferencias y las reacciones de los tejidos peri implantares en implantes inmediatos postextracción en alvéolos de molares mandibulares infectados o no infectados, con o sin colocación de injerto óseo. Métodos: Se colocaron cuatro implantes inmediatos postextracción de molares mandibulares con o sin infección en cuatro pacientes, fueron divididos en 2 grupos (n=2), uno sin injerto óseo y otro con injerto óseo. Se realizó controles clínicos y radiográficos a los 8 días y a los 4 meses de colocado el implante. Resultados: Ambos grupos presentaron oseointegración de los implantes con una taza de supervivencia del 100%. No se observó mayor diferencia en los cambios de nivel de la cresta ósea en sentido vertical ni horizontal. Conclusiones: Con las limitaciones del presente estudio, podemos concluir que la colocación de los implantes inmediatos postextracción en molares mandibulares con el uso o no de injerto óseo no presenta mayor diferencia.