An epizootic of focal epithelial hyperplasia (FEH) or Morbus Heck in a pygmy chimpanzee (Pan paniscus) colony is described. Papovavirus-like particles were observed in the nuclei of epithelial cells. Analysis of the DNA of the lesions revealed an episomal papillomavirus-specific band with a molecular size of approximately 8,000 bp. In situ hybridization under high stringency conditions showed cross-hybridization between the chimpanzee papillomavirus DNA and human papillomavirus (HPV) type 13. The latter virus is uniquely associated with oral disease in man. This is the first demonstration of the association of a HPV 13-related pygmy chimpanzee papillomavirus (PCPV) and oral epithelial hyperplasia in a nonhuman primate.