Genetic factors have been implicated in the aetiology of infraocclusion, but only three published reports describe infraocclusion of primary molars in twins. This case report describes the occurrence of infraocclusion in two pairs of twins. The distribution of affected teeth and the severity of infraocclusion were strikingly similar in each pair. The report provides further evidence of a genetic contribution to the aetiology of the condition, and also highlights the need to examine siblings, and especially twins, of children who present with an infraoccluded primary tooth.