Mistreatment by customers is a common occurrence for many frontline service employees. Although some evidence suggests that employees engage in dysfunctional workplace behaviors as a result of mistreatment, others studies have suggested that employees may cope with such negative experiences by helping others. Drawing on negative state relief theory, we conducted 2 studies to test these relationships and examine whether service employees cope with negative emotions arising from such daily customer mistreatment by engaging in helping others. In Study 1, daily surveys from 70 restaurant employees showed that daily customer mistreatment predicted the experience of negative moods the next morning, which, in turn, led to higher levels of coworker helping the next day. In Study 2, daily surveys from 54 retail employees showed that daily customer mistreatment led to higher customer helping the next day, but only when customer orientation was high. Our results further show that helping behavior was associated with elevated positive affective experiences and that the proposed relationships differ depending on whether customer mistreatment is measured at a daily or a cumulative perspective. Specifically, cumulative customer mistreatment over time decreased general helping. These findings are discussed in relation to employees' coping strategies towards acute and cumulative mistreatment.