In a consecutive series of minor surgical specimens from the anal canal, neuronal hyperplasia was found in nine of 56 haemorrhoidectomy specimens and in four of 23 fibrous polyps. In an additional series of 14 resections of the anal canal, neuronal hyperplasia was present in six cases, of which five showed haemorrhoids. In all cases, neuronal hyperplasia was located in the submucosa beneath squamous epithelium and extended over an area from 5 to 12 mm. Immunohistochemically, the foci of hyperplasia were found to consist of both neuronal and Schwann cell components. Staining for vasoactive intestinal peptide, neuropeptide Y and calcitonin gene related peptide, did not demonstrate any increased terminal density. It is suggested that anal neuronal hyperplasia in these cases represents an acquired lesion due to local mechanical influence.