In this study, we evaluated the influence of different forms of support (peer support, ventilation or defusing led by the ordinary group leader, and more formal debriefing sessions led by an external counselor) on mental health following traumatic experiences, using a prospective study design. The sample consisted of a Swedish battalion (N = 510), which was part of NATO’s implementation force in Bosnia in 1996. Preservice assessment was made of personality, sense of coherence, and mental health. One third of the soldiers experienced traumatic situations during their service. Results showed that poor mental health after service was related more to preservice mental health and sense of coherence than to trauma exposure and posttrauma support. Peer support followed by a defusing session had a positive effect on postservice mental health, although this did not apply to the individuals with the worst preservice mental health. The value of formal debriefings could not be evaluated due to insufficient data.