Monoamine oxidases (MAO) are an important component of the homeostatic machinery that maintains the levels of monoamine neurotransmitters, including dopamine, in balance. Given the imbalance in dopamine levels observed in HD, the aim of this study was to examine MAO activity in cellular models of HD and in patient dermal fibroblasts. We show that cells expressing mutant HTT exhibit increased MAO expression and activity. Using cellular stress paradigms, we further demonstrate that the increase in MAO activity in mutant cells is accompanied by enhanced susceptibility to oxidative stress and cell death. Treatment of mutant cells with MAO inhibitors ameliorated oxidative stress and reduced cell death. This study demonstrates abnormal MAO expression and activity and suggests a potential use for MAO inhibitors in HD.