Genome wide analysis revealed the miR-17/92 cluster as a STAT5 target. This cluster encodes six microRNAs, which predictably target genes that play a role in mammary gland development. In this study we have deleted the miR-17/92 cluster in mammary stem cells and evaluated in the mouse its function during mammary gland development. Loss of the miR-17/92 cluster did not affect mammary development from pre-puberty to lactation. Our studies demonstrated that while expression of the miR-17/92 cluster is under control of the key mammary transcription factor STAT5, its presence is not required for normal mammary development or lactation.