The authors examined whether smoking cessation and relapse were associated with changes in stress, negative affect, and smoking-related beliefs. Quitters showed decreasing stress, increasing negative health beliefs about smoking, and decreasing beliefs in smoking's psychological benefits. Quitters became indistinguishable from stable nonsmokers in stress and personalized health beliefs, but quitters maintained stronger beliefs in the psychological benefits of smoking than stable nonsmokers. Relapse was not associated with increases in stress or negative affect However, relapsers increased their positive beliefs about smoking and became indistinguishable from smokers in their beliefs. For quitters, decreased stress and negative beliefs about smoking may help maintain successful cessation. However, for relapsers, declining health risk perceptions may undermine future quit attempts.