Background: Lower parental nurturance is consistently associated with higher levels of youth antisocial behavior (ASB), but the etiology of this association remains unclear. To fill this gap, we employed a twin differences approach to illuminate the environmental and genetic origins of the association between parental nurturance and children's ASB. Methods: Participants were 2060 twins (49% female) ages 6-10 from the Michigan State University Twin Registry. Parental nurturance and youth ASB were assessed using multiple measures (e.g., questionnaires, interviews) and informant reports (e.g., twins, parents, teachers). Co-twin difference-score correlations were analyzed separately by zygosity using specification curve analysis, an exhaustive modeling approach that examined associations across all possible specifications of the nurturance and ASB data. Results: Parental nurturance demonstrated clear, negatively signed associations with youth ASB at the individual level. However, these associations generally did not persist within twin pairs. We observed no significant twin difference correlations within monozygotic (MZ) pairs and only a handful of significant twin difference correlations among dizygotic (DZ) pairs, in which the DZ co-twin who experienced more nurturance exhibited less ASB. Post-hoc analyses in these data revealed that these associations differed markedly from those with harsh parenting that suggested environmental influences on youth ASB. Conclusions: These results strongly argue against a causal influence of low parental nurturance on youth ASB, and instead suggest that genetic influences and shared environmental confounds underlie their association. Further, findings strongly suggest that different parenting behaviors are associated with child ASB via different etiologic mechanisms.