The proposition recently offered by S. E. Taylor and J. D. Brown (1988) that positive illusions foster mental health has garnered considerable attention and acceptance. However, the significant theoretical and applied implications of their view for mental health require a critical evaluation of their argument. An examination of the logic and empirical evidence used to relate mental health to three key positive illusions--unrealistically positive views of the self, illusions of control, and unrealistic optimism--failed to substantiate Taylor and Brown's thesis. Further survey of more recent studies on positive illusions and mental health also failed to lend support to the Taylor and Brown generalization. Close consideration of several assumptions underlying the formulation raises further questions regarding their thesis. The present article concludes that it remains unproven that positive illusions foster mental health.