The relation between women's timing of menarche and father absence was examined in a national probability sample of Great Britain (NATSAL 2000; N>5000). Current body mass index (as a proxy for childhood weight) was examined as a potential mediator of this relationship, along with the potential moderating role that siblings (e.g. number of older brothers) had on this relationship. As in a number of previous studies, an absent father (but not an absent mother) during childhood predicted an earlier age of puberty (i.e. an early menarche). There was no evidence that weight mediated this relationship or that siblings moderated it. Both a lower body mass index and more siblings (e.g. more younger sisters and brothers) were independent predictors of a later timing of puberty. The results confirm that certain psychosocial factors (i.e. father absence; presence of siblings) may affect the timing of sexual maturation in adolescent girls.