Mustard gas is a simple molecule with a deadly past. First used as a chemical weapon in World War I, its simple formulation has raised concerns over its use by terrorist organizations and unstable governments. Mustard gas is a powerful vesicant and alkylating agent that causes painful blisters on epithelial surfaces and increases the incidence of cancer in those exposed. The mechanism of mustard gas toxicity and tumorigenesis is not well understood but is thought to be mediated by its ability to induce oxidative stress and DNA damage. Interestingly, several proteins that have been shown to either be targets of mustard gas or mediate mustard gas toxicity have also been shown to regulate centrosome duplication. Centrosomes are small nonmembrane-bound organelles that direct the segregation of chromosomes during mitosis through the formation of the bipolar mitotic spindle. Cells with more or less than two centrosomes during mitosis can segregate their chromosomes unequally, resulting in chromosome instability, a common phenotype of cancer cells. In our studies, we show that subtoxic levels of 2-chloroethyl ethylsulfide (2-CEES), a mustard gas analog, induce centrosome amplification and chromosome instability in cells, which may hasten the mutation rate necessary for tumorigenesis. These data may explain why those exposed to mustard gas exhibit higher incidences of cancer than unexposed individuals of the same cohort.