Adenovirus type 11 (Ad11), a member of the human adenovirus species B (HAdV-B), has a tropism for the urinary tract. The genome of Ad11 was found to comprise 34 794 bp and is 1141 bp shorter than the Ad5 genome of species HAdV-C. The G+C content of the Ad11 genome is 48.9 %, whereas that of Ad5 is 55.2 %. Ad11 and Ad5 share 57 % nucleotide identity and possess the same four early regions, but the E3 region of Ad11 could not be divided into E3A and E3B. The late genes of Ad11 and Ad5 are organized into six and five regions, respectively. Thirty-eight putative ORFs were identified in the Ad11 genome. The ORFs in the late regions, the E2B region and IVa2 show high amino acid identity between Ad11 and Ad5, whereas the ORFs in E1, E2A, E3 and E4, protein IX and the fibre protein show low amino acid identity. The highest and lowest identities were noted in the pre-terminal protein and fibre proteins: 85 % and 24.6 %, respectively. The E3 20.3K and 20.6K ORFs and the L6 agnoprotein were present in the Ad11 genome only, whereas the E3 11.6K cell death protein was identified only in Ad5. All ORFs but the E3 10.3K and L4 pVIII protein vary not only in composition but also in size. Ad11 may have a higher vector capacity than Ad5, since it has a shorter genome and a shorter fibre. Furthermore, in the E3 region, two additional ORFs can be deleted to give extra capacity for foreign DNA.