['This study explored how multiple bioecological constructs operate to explain health-risk behaviors in late adolescence and to test for moderator effects of gender.', 'This was a descriptive, cross-sectional study with a convenience sample of 437 predominately Caucasian late adolescents with an average age of 19 years who lived in Northern California.', 'Parental Attachment, Shyness, Loneliness, Law Abidance, and Youth Risk Behaviors were measured with self-report tools and analyzed using structural equation modeling.', 'Confirmatory factor analysis indicated that the data fit the model well. Analysis of group differences revealed that gender moderated the relationships among the measured variables; thus, data were analyzed in independent gender-based models. Structural modeling demonstrated good model fit for each gender. Shyness and parental attachment each were associated with loneliness. Loneliness was associated with smoking. Loneliness linked the relationship between shyness, parental attachment, and smoking. Parental attachment was associated with law abidance. Law abidance was associated with sexual behaviors for female adolescents only.'] Does mediation of late adolescent health-risk behaviors and gender influence?