Health-risk behaviors associated with increased risk of suicide are more prevalent in old-for-grade students compared to age-appropriate-for-grade peers; however, the association between old-for-grade status and suicidal behavior is largely unknown. This study investigated sex-specific differences in suicidal ideation, planning, attempts, and other risk behaviors by old-for-grade status. Secondary analyses utilizing bivariate and logistic regression methods for complex samples were conducted using data from the 2011, 2013, and 2015 National Youth Risk Behavior Survey for 16,579 female and 17,282 male high school students in grades 9 through 11. Among both males and females, students considered old-for-grade reported increased drug use, feeling sad/hopeless, violence, sexual activity, and limited/no seatbelt use compared with their peers. Old-for-grade students were also more likely to report a suicide attempt with increased suicidal ideation and planning observed only in old-for-grade males. Associations between old-for-grade status and suicide risk-related outcomes were attenuated in both sexes after adjusting for demographic characteristics and other health-risk behaviors. Findings suggest that common risk factors (e.g., sadness, substance use) may explain increased rates of suicidal behaviors in old-for-grade students.