Research indicates that veterans would like their families to be more involved in their mental health care. While Department of Veteran Affairs (VA) policy requires certain providers to discuss veterans’ interest in family involvement in their mental health care, no published studies have examined the associations between family involvement and mental health outcomes in routine VA mental health care. This study assessed posttraumatic stress disorder (PTSD) symptoms before and after veterans’ first family session to test whether symptoms changed after family inclusion. The study used administrative data from VA medical records from 2008–2013. Veterans included in the present study sample had at least one assessment of PTSD symptoms in the year prior to and following their first family session (N = 6,107). Multilevel models tested whether PTSD symptoms changed over time. Moderator analyses assessed whether the change in PTSD symptoms differed depending on the veteran’s gender, psychiatric comorbidities, and intensity of family involvement following the first session. On average, results showed statistically, but not clinically, significant reductions in PTSD symptoms after the first family session. Women veterans, veterans with comorbid depression, and those who had eight or more family sessions showed stronger symptom reductions than others. This study provides provisional evidence that family involvement is associated with PTSD symptom reduction.