Relationships between secondary traumatic stress (STS) symptoms and therapist characteristics and assignment variables were examined for 81 disaster mental health (DMH) workers who responded to the terrorist attacks of September 11, 2001. Higher STS was associated with therapist variables of heavier prior trauma caseload, less professional experience, youth, and therapist's discussion of his or her own trauma or trauma work in his or her own therapy. Therapist gender and personal trauma history were not significantly related to STS. Assignment variables associated with higher STS included longer length of assignment and more time spent with child clients, firefighters (who suffered great losses in the tragedy), or clients who discussed morbid material. Recommendations for practice include informing DMH recruits of therapist risk factors and assigning at-risk DMH workers to lower-risk assignments.