Objective: Despite the high prevalence of posttraumatic stress disorder (PTSD) among veterans treated at Department of Veterans Affairs (VA) facilities, rates of initiation of mental health treatment and persistence in treatment are unknown. This study examined outpatient treatment participation among veterans with a recent PTSD diagnosis and treatment differences according to the VA sector in which they received the diagnosis (PTSD specialty treatment program, general mental health clinic, and general medical clinic). Methods: Administrative data for 20,284 veterans who had received a diagnosis of PTSD at VA facilities were analyzed to determine rates of treatment initiation (any psychotropic prescription, an antidepressant prescription, behavioral counseling, and either a prescription or counseling) and maintenance of pharmacotherapy (at least four 30-day supplies), and counseling (at least eight visits) for the six months after diagnosis. Results: Approximately two-thirds of the sample initiated treatment: 50% received a psychotropic medication and 39% received some counseling; 64% received either medication or counseling. About half of those given medication (54%) received at least a four-month supply, and 24% of those given counseling had at least eight sessions. Overall, 33% received minimally adequate treatment. Initiation, type, and duration varied by treatment sector: receipt of a diagnosis in a PTSD specialty program or a mental health clinic conferred small but significant benefits over receipt in a general medical clinic. Conclusions: Greater availability of mental health specialty services, particularly PTSD services, may be needed to ensure that veterans receive minimally adequate treatment after a PTSD diagnosis.