Abstract: Objective: The objective was to examine differences by age in mental health treatment initiation in Veterans Health Administration (VA) primary care patients after positive posttraumatic stress disorder (PTSD) screens.Methods: This was a retrospective cohort study of 71,039 veterans who were administered PTSD screens during primary care encounters in 2007 at four Pacific Northwest VA medical center sites and who had no specialty mental health clinic visits or PTSD diagnoses recorded in the year before screening. Main outcome measures were attendance of any specialty mental health clinic visits or receipt of any antidepressant medication in the year after a positive PTSD screen.Results: Older veterans, compared with veterans less than 30 years old, were less likely to attend any specialty mental health visits after positive PTSD screens [adjusted odds ratios (ORs) ranged from .57 to .12, all P<.001], and veterans 75 years and older were less likely to receive any antidepressant medication (adjusted OR=.56, P<.001).Conclusions: Initiation of mental health treatment among veterans who screen positive for PTSD varies significantly by age. Further research should examine whether this is due to differences in base rates of PTSD, treatment preferences, provider responses to screens or other age-related barriers to mental health treatment.