Lesions caused by an avian poxvirus were identified on the face and nares of fledgling white-tailed tropicbirds (Phaethon lepturus catesbyi) in the natural environment on Bermuda. Between 1958 and 1978,6 of 81 fledglings found off the nest and unable to fly at departure time had lesions suggestive of poxvirus infection. More detailed nest-site surveys from 1974 to 1978 indicated an overall prevalence of less than 0.5%, involving the fledgling population only.