Gottfredson and Hirschi's General Theory of Crime contends that low self-control interacts with opportunity to produce criminal and analogous behaviors. Although several theoretical and empirical attempts have been aimed at assessing the general theory, researchers have been slow to examine one of the central postulates of the general theory: the stability postulate. Gottfredson and Hirschi contend that once established by ages eight to ten, self-control remains relatively stable over the life-course. In the only study to address this question, Arneklev, Cochran, and Gainey found that self-control levels were relatively stable in a four month test-retest among college students. In this article, the work of Arneklev et al. is extended and examination is made of the stability postulate in childhood, adolescence, and early adulthood. Using a national probability sample, as well as behavioral and attitudinal measures of self-control, the results offer mixed support for Gottfredson and Hirschi's stability postulate. Theoretical and future research directions are advanced.