Stage IV grade C localized periodontitis (pre-puberal localized aggressive periodontitis/LPP), an extremely rare form of periodontal disease, occurs in otherwise healthy individuals (no signs of dental plaque/calculus) due a hyper-aggressive auto-immune response to high periodontopathic bacteria levels. Methods: A 4-year-old Caucasian girl with unusual high mobility of temporary lower left canine and localized gingival inflammation was misrecognized by multiple clinicians (initially diagnosed with hypophosphatasia, genetic and metabolic disorders, all turning negative), over a period of 4-6 month, despite initial radiographs showing clear pathognomonic signs. LPP diagnostic was made by the last clinician, but by now the tooth was lost. Similar inflammation signs appeared around the lower temporary right canine. X-ray examination showed similar bone and periodontal loss as previously seen, while periodontopathic bacteria tested highly positive. The patient received both mechanical cleaning and ten days systemic antibiotic treatment (Augmentin and Metronidazole). Results: Two months after, inflammation signs disappeared, with periodontal regeneration radiologically present, and only small periodontopathic bacteria precursors concentrations. Conclusions: Despite initial periodontal loss, an adequate treatment can keep under control an LPP disease. Moreover, bone and periodontal regeneration appears if periodontopathic bacteria scores are kept lower, showing the importance of fast adequate diagnostic and treatment.