The complete genomic sequence of the Lactococcus lactis virulent phage ul36 belonging to P335 lactococcal phage species was determined and analyzed. The genomic sequence of this lactococcal phage contained 36,798 bp with an overall G+C content of 35.8 mol %. Fifty-nine open reading frames (ORFs) of more than 40 codons were found. N-terminal sequencing of phage structural proteins as well as bioinformatic analysis led to the attribution of a function to 24 ORFs (41%). A lysogeny module was found within the genome of this virulent phage. The putative integrase gene seems to be the product of a horizontal transfer because it is more closely related to Streptococcus pyogenes phages than it is to L. lactis phages. Comparative genome analysis with six complete genomes of temperate P335-like phages confirmed the heterogeneity among phages of P335 species. A dUTPase gene is the only conserved gene among all P335 phages analyzed as well as the phage BK5-T. A genetic relationship between P335 phages and the phage-type of the BK5-T species was established. Thus, we proposed that phage BK5-T be included within the P335 species and thereby reducing the number of lactococcal phage species to 11.