Hirschi's (1969) control theory has received much empirical support and, as a consequence, has become one of the dominant theories of delinquency. Virtually all tests of the theoty, however, have been conducted with cross-sectional data This is a serious problem since there is good reason to believe that delinquency may have a causal impact on social control. This paper describes a longitudinal test of Hirschi's theory using panel data from a national sample of adolescent boys. Data indicate that the social control variables explain only 1%-2% of the variance in future delinquency, suggesting that cross-sectional studies have exaggerated the importance of Hirschi's theoty. Possible reasons for the small longitudinal effect of the control variables are discussed.