Periodontitis, compared to gingivitis, is a relatively uncommon disease in children, and the accumulation of plaque is not the common cause. Thorough examinations are required to reveal the real cause for periodontitis in children which may involve local factors or other underlying systemic diseases. However, the etiology of periodontitis is multifactorial and undetermined causes are still present. This case report is about a two-year follow-up of a five-year-old boy with atypical localized aggressive periodontitis that caused premature loss of bilateral mandibular canine, and the discussion focuses mainly on the etiology. Although periodontitis is a relatively rare condition in children, it may result in acute symptoms and tooth loss, which should not be overlooked.