Gottfredson and Hirschi's general theory has generated an abundance of research examining the effects of low self-control on crime and analogous behaviors. Less research, however, has focused on the factors that contribute to the development of low self-control. Gottfredson and Hirschi maintain that ineffective parents are the sole cause for the emergence of low self-control. At the same time, they disregard the possibility that low self-control has a biological or genetic component. This article extends prior research and examines the effects of birth complications and parental involvement on low self-control. Using a sample of twin children, the authors find that parental involvement is only weakly and inconsistently related to low self-control. On the other hand, although most of the birth complications had no appreciable effect on low self-control, anoxia (oxygen starvation) emerged as the strongest and most consistent predictor of low self-control.