Recall of patients who had been treated by a human immunodeficiency virus (HIV)-infected surgeon uncovered 1 previously unknown HIV-seropositive person. Nucleotide sequencing of the gag gene and maximum likelihood phylogenetic analysis were used to investigate the relationships among sequences from the surgeon, the patient, and an anonymous blood donor from whom the patient had received blood products. The likelihoods of all possible pathways of transmission linking these persons were estimated. On these data, transmission from the surgeon to the patient was significantly less likely than from the blood donor to the patient. It is concluded that none of the recalled patients were infected by the surgeon.