This study compared the aetiology and pathological characteristics of adult and childhood adenoid hypertrophy (AH). Clinical and morphological features and accompanying otolaryngological pathologies were recorded in 40 adults and 23 children undergoing adenoidectomy for obstructive AH. Both AH forms were similar in terms of symptomatology and associated inflammations. There were, however, significant differences in otitis media rate, with effusion and dullness, and retraction in the eardrum both more prevalent in childhood AH. Adult AH was associated with nasal septum deviation in 25.0% of patients. Histopathological features of adenoidal lymphoid tissue were dissimilar in the two groups: numerous lymph follicles with prominent germinal centres was the chief finding in childhood adenoids, whereas adult adenoids showed chronic inflammatory cell infiltration and secondary changes (e.g. squamous metaplasia). These results underline the importance of considering AH as a cause or contributing factor in nasal obstruction and related pathologies in adults and supports the theory that it represents a long-standing inflammatory process rather than being a novel clinical entity.