Background and aims: To reconcile an inconsistency in the disordered gambling literature by revisiting a previous study that claimed to find evidence for large gender differences in the magnitude of genetic and environmental influences. Design: Univariate structural equation twin models were fitted to decompose the variation in gambling behavior into additive genetic, shared environmental and unique environmental influences. Setting: United States. Participants: Participants were 1196 same-sex and unlike-sex twins (18-28 years of age, 49% male, 51% female) from the National Longitudinal Study of Adolescent Health (Add Health). Measurements: Eight questions about normative and problematic gambling involvement were assessed by in-person interview. Although disordered gambling symptoms were assessed, the number of individuals who were administered these questions precluded twin analysis, including analysis of potential gender differences. Of the eight questions, only three were deemed usable for twin analysis-these were all questions about normative gambling involvement. Findings: Individual differences in (non-disordered) gambling involvement were explained completely by family [C = 38% (30-46%)] and unique environmental factors [E = 62% (54-70%)]. There was no evidence for genetic factors (A = 0), nor was there evidence for sex differences (DELTAchi2 = 1.23, d.f. = 2, P = 0.54). Conclusions: There appears to be no evidence for gender differences in the genetic contributions to disordered gambling. Family environment appears to play a significant role in explaining individual differences in (non-disordered) gambling involvement among emerging adults.