A laryngeal squamous cell carcinoma was observed in a 12-year-old child. There was no history of preceding papillomatosis or radiotherapy. We searched for an association with human papillomavirus (HPV). The resected specimens were assayed for infection with HPV types 11, 16, 18, 31, 33, 35, 39, 42 by in situ hybridization, and for HPV types 6, 16, 18, 33 by Southern blotting. In addition, cervical swabs of the mother were examined for HPV infection by filter in situ hybridization. Coinfection by HPV types 18 and 33 could be demonstrated by in situ hybridization, with homogeneous infection of both tumor and adjacent epithelial cells by HPV 33 and focal infection of only invasive cancer by HPV 18. Southern blot testing confirmed a high viral copy number of HPV 18 DNA. Examination of the mother at the time of tumor diagnosis revealed no evidence of HPV-related lesion in the lower genital tract. In this child, coinfection by at least two HPV types is the only evaluable risk factor for laryngeal carcinoma. Coinfection by two HPV types might substitute for carcinogenic cofactors normally present in adult laryngeal carcinomas.