We examined the imprinting status of the insulin-like growth factor II gene (IGF2) in a series of 20 human breast disease samples to determine if disrupted imprinting (as evidenced by biallelic expression), was a demonstrable mechanism of altered gene expression. These samples included benign (n = 7) and malignant breast lesions (n = 13). Biallelic expression of IGF2 was detectable in 67% of benign and 60% of malignant informative breast lesions. Three informative reduction mastectomies displayed normal IGF2 imprinting. The presence of this alteration in human breast tissue is a novel finding, and may contribute to tumorigenesis, possibly by favouring an enhanced proliferative milieu, during which additional mutations could occur.