Malignant osteopetrosis generally begins in utero and often results in stillbirth. Besides, failure to thrive, increased bone fragility resulting in frequent fractures and recurrent bone infections are the other characteristic features. Infections after tooth extraction and fracture of the sclerotic bone following mild trauma are serious complications, as these ordinarily common problems are very difficult to treat in such patients. Poor bone vascularisation and reduced local defences prolong the defensive response. A rare case of malignant osteopetrosis in a 19-year-old girl, who presented with the complication of osteomyelitis of the mandible following tooth extraction, is presented. The case is of interest for two reasons: it is very rare for a case of malignant osteopetrosis to survive until adulthood and to be aware of the potential dental and oral complications of the disorder.