Military staff performance may be inferior due to several reasons. The purpose of the present survey was to study the impact of stress reactions, personality factors, situation awareness, and maladaptive group dynamics on the quality of the decision-making in Swedish high-level military staffs. Participants were mainly captains and majors, but also lieutenant colonels and colonels took part (n = 256, 61 % response rate). A mainly self-made questionnaire was administered in two staff exercises. Maladaptive group dynamics, stress exposure, lack of situation awareness, and negative stress reactions were the strongest predictors of poor staff performance, while personality had less impact.