Posttraumatic stress disorder (PTSD) is associated with greater risk of developing comorbid depression. However, little is known about the relationship between specific PTSD symptom clusters and comorbid depression. Approximately 4 years after the World Trade Center (WTC) attacks, we examined the association between PTSD symptom clusters and depression severity among 64 mothers directly exposed to the WTC attacks. Severity scores were computed for each PTSD symptom cluster by summing symptom frequency. Partial correlations with depression severity were calculated separately for PTSD symptom clusters, controlling for demographic variables, time elapsed since the attacks, WTC attack exposure, meeting PTSD criterion A, and the other cluster scores. Higher arousal symptom cluster scores were significantly correlated with persistent depression, but the re-experiencing and avoidance symptom clusters were not. Subsequent analyses isolating shared symptoms of PTSD and depression from those unique to PTSD suggest a complex interrelationship among symptoms of arousal, numbing, and depression.