One third of all children are born to unmarried mothers and over one half of children will spend some time in a single-parent family. In fact, single-father families are the fastest growing family form. Using data from the 1995 National Longitudinal Survey of Adolescent Health, the authors extend prior research that has investigated the effects of growing up in a two-parent versus single-mother family by examining adolescent delinquency in single-father families, too. This strategy helps us to identify the mechanisms through which living with a single parent increases delinquency, notably, whether the effect is predominantly a function of parental absence (i.e., one versus two parents) or parental gender (i.e., single mother versus single father). The results indicate that adolescents in single-parent families are significantly more delinquent than their counterparts residing with two biological, married parents, although these differences are reduced once the authors account for various family processes. Furthermore, family processes fully account for the higher levels of delinquency exhibited by adolescents from single-father versus single-mother families. (Contains 5 tables and 2 notes.)