Mosaic loss of chromosome Y (mLOY) refers to the condition in male individuals in which a detectable fraction of cells lose the Y chromosome. Prevalent in haematopoietic cells, this common somatic mutation is associated with decreased longevity and an increased risk of age-related diseases, including cardiovascular disease. Haematopoietic mLOY provides further insight into the sex-specific disparities that exist in disease susceptibility.