Adenovirus type 35 (Ad35) is an uncommon group B adenovirus that has been isolated nearly exclusively from immunosuppressed hosts. In our series of 46 patients with Ad35 isolates, 36 had AIDS or AIDS-related complex (ARC), seven patients were immunocompromised because of other diseases, and three patients were "normal." Neither patients with AIDS or ARC made specific antibody to Ad35, whereas antibody was present in one immunocompetent host and one renal transplant recipient. All isolates were identified as Ad35 by using genomic analysis with the restriction endonuclease SmaI, but many viruses exhibited other group B hemagglutinins, a property of the fiber protein. Further analysis of DNAs from 40 of these isolates, mapped by using the enzymes BamHI, HpaI, and PstI, revealed a total of 14 genomic variants from the Ad35 prototype. Seven of these genomic types, with either Ad7 or Ad11 hemagglutinin, had corresponding restriction site differences within the fiber gene, a result consistent with recombination events with other group B adenoviruses.