Based on a multifunctional model of perfectionism (E. Chang, Cognitive Ther Res, 30:677–697, 2006), this study examined the relations between performance perfectionism, optimism, pessimism, and positive psychological functioning (e.g., self-acceptance, positive relations with others, and personal growth) in a sample of 246 middle-aged adults. Results from correlational analyses indicated that positive aspects of performance perfectionism, especially positive self-oriented performance perfectionism, were positively associated with positive psychological functioning, whereas negative aspects of performance perfectionism, especially negative selforiented performance perfectionism, were negative associated with positive psychological functioning. In addition, results of conducting regression analyses indicated that although optimism and pessimism were significant predictors of positive psychological functioning in middle-aged adults, the inclusion of positive and negative self-oriented performance perfectionism significantly augmented the prediction models examined. These findings point to a need to consider multiple determinants (including optimism, pessimism, and performance perfectionism) when studying positive psychological functioning in middle-aged adults.