Described is a composition comprising a plurality of recombinant adenovirus particles, being a recombinant human adenovirus of serotype 5, 26, 34, 35, 48, 49 or 50, or a recombinant simian adenovirus, characterized in that the genomes of essentially all adenovirus particles in the composition comprise as the 5′ terminal nucleotides the nucleotide sequence: CTATCTAT (nucleotides 1-8 of SEQ ID NO:7). Also described are methods to produce such compositions.