Intergenerational transmission of trauma (ITT) has been documented among offspring of parents exposed to war, genocide, and interpersonal violence, yet little is known about ITT among families of World Trade Center responders (WTC-R). The aftermath of 9/11 terrorist attacks provides a unique naturalistic context for examining long-term psychological outcomes among now-adult offspring raised during periods of parental trauma exposure and recovery. The WTC-R cohort comprised traditional first responders (i.e., law enforcement officers) and nontraditional recovery workers, among whom those with PTSD were invited to complete an online survey and recruit their adult offspring. Parents and offspring completed standardized assessments of mental health, including depression, anxiety, PTSD, panic disorder, substance use, and lifetime traumatic experiences, as well as measures of social support, family relationships, and quality of life. Generalized Estimating Equations (GEE) models were used to examine associations between parental 9/11-related exposure, current parental psychopathology, and offspring mental health outcomes, with moderation by responder occupational category. Greater parental 9/11 exposure was associated with a higher likelihood of PTSD, anxiety, and panic symptoms among adult offspring. Current parental PTSD and depression were significantly associated with offspring PTSD and depression, respectively. Poor parent-offspring relationships were associated with offspring depression, PTSD, and alcohol use disorder. Several associations were moderated by occupational subgroup, suggesting differential vulnerability linked to the nature and context of exposure. These findings demonstrate enduring intergenerational mental health effects more than two decades after 9/11, highlighting how parental trauma exposure, ongoing psychopathology, and family relational functioning collectively shape outcomes in WTC-R offspring.