This study examined the prevalence and predictors of posttraumatic stress disorder (PTSD) symptoms in 70 men and women treated with bone marrow transplantation for cancer. Findings indicated that the number of symptoms present ranged from 0 to a possible high of 17 (M = 3.0, SD = 3.9). As predicted. lower social support and higher avoidance coping I month pretransplant predicted greater PTSD symptom severity an average of 7 months posttransplant. These variables remained significant predictors of symptom severity even after accounting for pretransplant levels of psychological distress. Additional analyses indicated the presence of a significant interaction between social support and avoidance coping, with patients high in avoidance coping and low in social support reporting the most severe symptoms. These findings identify patients at risk for psychological disturbance posttransplant and can serve to guide future intervention efforts.