Adult testicular dermoid tumours are rare tumours with no reported potential for recurrent or metastatic spread. Despite this they are currently classified as mature teratoma and managed as if they have equivalent malignant potential. This report describes two cases of adult mature teratoma of dermoid type and questions the classification and pathogenesis of this disease. In one of the cases there was a clear history of a testicular lump arising pre-pubertally, raising the possibility that some adult dermoid tumours may in fact be pre-pubertal teratomas that have persisted into adulthood. Classification as a mature teratoma carries with it a follow-up regimen that includes numerous radiological investigations with their attendant radiation exposure. A positive histological diagnosis and separate classification of adult dermoid tumours would allay clinical fears of recurrence and metastasis and negate the need for repeated radiological investigations.