Objective: The aim of this study was to examine the long-term trajectories and interrelationships of posttraumatic stress disorder (PTSD) symptom clusters (intrusion, avoidance, and hyperarousal) in clinical and nonclinical groups of war veterans. Method: Six hundred seventy-five Israeli veterans from the 1982 Lebanon War were assessed. The clinical group consisted of 369 who had combat stress reaction (CSR) during the war, and the nonclinical group consisted of 306 veterans with no antecedent CSR. The 2 groups were matched in age, education, military rank, and assignment. They were prospectively evaluated 1, 2, and 20 years after the war. Results: The clinical group endorsed a higher number of symptoms than the nonclinical group, both cross-sectionally and across time. In both the clinical and nonclinical groups, the clusters of intrusion, avoidance, and hyperarousal were interrelated at any given point in time and across 20 years. In both groups, avoidance was found to be a particularly stable symptom cluster over time. Finally, hyperarousal levels 1 year after the war were found to play an important role in both groups, as they predicted future avoidance and intrusion symptoms. Conclusions: The findings of this study suggest that PTSD is not a monolithic disorder, as symptom clusters differ in several important aspects. Also, the course and severity of symptoms differ between clinical and nonclinical groups. Finally, practitioners are encouraged to focus on the identification and treatment of early hyperarousal due to its prominent role in the development of other PTSD symptoms.