Background.The human T-cell lymphotrophic virus (HTLV) causes adult T-cell leukemia-lymphoma, tropical spastic paraparesis-HTLV type I, and associated myelopathy.Methods.An analysis was performed of serum samples from a multiorgan donor and the five recipients. Also studied was the donor’s family and the partner of one of the renal recipients. Serologic detection of anti-HTLV antibodies was carried out by enzyme immunoassay and Western blot to confirm and discriminate between HTLV types. Analysis of proviral DNA was performed by polymerase chain reaction and sequenced in the long terminal repeat region and theenvgene. Peripheral blood mononuclear cell samples from all the recipients of the HTLV-I–positive organs and the donor’s mother were studied.Results.Two years after transplantation, three organ recipients positive for antibodies to HTLV-I were detected (two kidney transplants and one liver). All the recipients’ serum samples were negative at the time of transplantation except those from the multiorgan donor. The donor’s mother was born in Venezuela and was confirmed positive for antibodies to HTLV-I. The remaining family members were negative. HTLV-I DNA sequences were recovered, amplified, and sequenced from all the samples from the HTLV-I–positive recipients and the donor’s mother. The homology of HTLV-I sequences was 100% in all cases.Conclusions.The authors are reporting the first documented case of HTLV-I infection in several transplant recipients sharing the same donor. The donor was infected by vertical transmission. HTLV-I infection has devastating consequences for some immunocompromised organ recipients. This emphasizes the need for a systematic survey of HTLV antibodies in all potential donors.