A 61 year old woman died of diffuse interstitial adenovirus pneumonia 55 days after receiving a cadaveric renal allograft. The adenovirus was serologically distinct from the 33 known human adenovirus serotypes and appears to represent a new human adenovirus. Pathologic and virological findings indicate that the pneumonia was only one manifestation of a disseminated infection, the source of which may have been a latent adenovirus infection preexisting in the donor kidney. The establishment of the etiologic diagnosis in this case, which was complicated by the presence of oculocutaneous and esophageal herpes simplex virus infection as well as focal pulmonary aspergillosis, required coordinated histopathologic and virological investigation. Our findings demonstrate that severe viral infections in transplant recipients are not caused exclusively by members of the herpesvirus group.