Oral screening and treatment of existing oral disease before bone marrow transplantation have been reported to decrease the incidence of infectious complications during bone marrow transplantation. Information about the adverse sequelae of specific preexisting oral diseases during bone marrow transplantation is lacking. The presence of postendodontic periapical radiolucencies may suggest recurrent or latent infection. The purpose of this study was to compare the effect of endodontic treatment with nontreatment of asymptomatic postendodontic periapical radiolucencies on the frequency of infectious oral complications during bone marrow transplantation. The records of 276 patients undergoing bone marrow transplantation examined between July 1988 and June 1991 were reviewed retrospectively. Twenty-three postendodontic periapical radiolucencies were identified in 8 women and 15 men. The mean age of patients was 41 years (range, 25 to 58 years). Fourteen of the lesions were untreated, and nine were treated before bone marrow transplantation. When outcomes of transplant complications were compared, neither increased systemic infection as measured by neutropenic days febrile nor local oral infectious complications were significantly different. These results suggest that nontreatment of asymptomatic postendodontic periapical radiolucencies does not increase the incidence of infectious complications during bone marrow transplantation.