Aggressive periodontitis is an especially severe and rapidly progressive disease (0.5–1% of the population in developed countries). This disease may affect patients at any age and begins often in prepuberty. The disease is characterised by family aggregation and rapid loss of attachment tissues. The extent of the disease is not often consistent with the amount of plaque on the teeth. If left undiagnosed and untreated, the patients may lose teeth already before the age of 20.