Gross stress incidents are typically sudden and unexpected, may constitute a threat to officer survival, may involve the loss of a partner or a physical ability, and may disrupt the officer's values or assumptions about his/her environment or other people. Reactions to such incidents constitute posttraumatic stress disorder (PTSD), which is manifested in three phases: the impact phase, which begins with the onset of the incident and continues until it no longer exerts a direct effect; the recoil phase, which begins with the removal of the impact stress and lasts until the officer resumes routine activities; and the posttraumatic phase, when the officer manifests symptoms of being unable to cope with the lingering impacts of the incident. Clinicians undertaking the treatment of officers with PTSD should differentially diagnose three types of reactions: normal stress reaction, severe stress reaction with healthy premorbid adjustment, and stress reaction with preexisting condition or impairment. A thorough understanding of these reactions produces a more timely and appropriate intervention. A case illustration of an officer's PTSD and its treatment and 10 references.