Untreated mental illness is an enormous problem in civilian and military populations. This paper reviews the literature on 1) methods and controversy related to defining the need for mental health treatment at a population level, 2) studies examining the relationship between mental disorder diagnoses and self-perceived need for mental health treatment, and 3) studies examining attitudes and barriers toward mental health care. Similar to civilian populations, the few studies in military samples have found that the majority of soldiers meeting criteria for a mental disorder do not receive mental health treatment or perceive a need for treatment. Attitudinal barriers (e.g., I would be seen as weak; a wish to solve the problem on their own) are more commonly endorsed than structural barriers (e.g., cost of services) toward seeking mental health care. Implications for future research and interventions are discussed.