Molecular, histopathological, and clinical studies were carried out on a series of 79 laryngeal papillomas (LP) from 36 patients in order to investigate the hypothesis that juvenile and adult LP may represent a biological entity causally related to Human papilloma virus (HPV) infection. Using in situ hybridization with biotin-labelled probes and polymerase chain reaction, we detected human papilloma virus (HPV) 6/11 in 28 of 29 juvenile LP, in 26 of 30 adult multiple, and in 17 of 20 adult solitary LP. None of LP was found to harbour HPV types 16, 18, 31, 33, and 51. There were no clear-cut histological differences between juvenile and adult LP, the presence of koilocytosis was equally observed in both, and there was no prevalent type of epithelial hyperplasia in either form, except that all three cases of atypical hyperplasias (precancerous lesions) were found among adult patients. During a 14 year follow-up, no carcinomatous transformation of LP was observed. All juvenile LP in our study had frequent recurrences of the disease, however, numerous surgical procedures were also required in 16 of 27 adult patients. Our study supports Lindeberg's hypothesis of a similar pathogenesis for all forms of LP caused by the HPV types 6/11.