Parenting behaviors are associated with adolescent suicidal ideation (SI), but few studies have examined this relation longitudinally or investigated underlying mechanisms. We investigated a moderated mediation model to evaluate perceived burdensomeness as a mediator in the longitudinal relation between parenting behavior (warmth and verbal hostility) and adolescent SI. We hypothesized that this association would be particularly strong among adolescents with greater functional impairment. The sample included 147 adolescents (Mage = 14.9, Age Range = 12-18 years, 76.2% female) and a primary caregiver (Mage = 43.5, Age Range = 27-60 years, 81.4% female) enrolled in a clinical trial. Caregivers completed measures of warmth and verbal hostility (PCPR) and adolescents completed measures of functional impairment (CDI-2), perceived burdensomeness (INQ), and SI (SIQ-JR) at baseline, 12 and 18 months. Two moderated mediation path analyses, one for each parenting behavior, were conducted. Age, sex, treatment condition, baseline and 12-month SI, baseline perceived burdensomeness, and the alternate baseline parenting behavior were included as covariates. Neither model yielded a significant direct effect between baseline parental verbal hostility or warmth and 18-month SI. However, lower warmth and higher verbal hostility were positively associated with 18-month SI indirectly through greater 12-month perceived burdensomeness among youth with relatively higher levels of functional impairment. Perceptions of burdensomeness are a mechanism by which low parental warmth and high parental verbal hostility contribute to SI, but only among youth with greater functional impairment. Interventions to address youth perceptions of burdensomeness may be beneficial, particularly for the most highly impaired youth.