Comparative genomic hybridization assays and compositions for use in practicing the same are provided. In the subject methods, at least first and second genomic templates are prepared from first and second genomic sources using an amplification reaction that employs a highly processive polymerase, where the amplification reaction produces amplification products having an average molecular size of at least about 10 kb with substantially no amplification bias. The resultant templates are then employed to produce at least first and second probe nucleic acid populations. The resultant probe nucleic acid populations are then contacted with a plurality of oligonucleotide target elements immobilized on a solid support surface and the binding of at least first and second populations is then evaluated. Also provided are kits for use in practicing the subject methods.