Double-strand breaks are one of the most critical DNA lesions with respect to cell-death and preservation of genomic integrity. Rapid phosphorylation of the histone variant H2AX at Ser-139 to form γH2AX is an early cellular response to DNA double-strand breaks. Visualization of discrete γH2AX foci using immunofluorescence-based assays has provided a sensitive and effective method for detecting DSBs which may be implicated in various pathologies including cancer, age-related diseases, chronic inflammatory diseases and ischemia-reperfusion injury. In this review, the potential utility and significance of γH2AX as a molecular marker of aging and disease is analyzed.