- The purpose of the study was to determine whether post traumatic stress disorder (PTSD) with Major Depressive Disorder (MDD) among urban public transit employees who were exposed to a workplace traumatic event is associated with greater PTSD severity over the 6-month follow-up period compared to PTSD without MDD, and also to identify predictors of PTSD severity among these employees. Information about Axis-I diagnosis and PTSD severity were collected from the SCID-I and the Modified PTSD Symptom Scale (MPSS) respectively. PTSD without MDD (N = 29) and PTSD with MDD (N = 37) groups were not significantly different in terms of PTSD severity. The severity of depression (p = 0.01), female (p = 0.01), non-Caucasian (p = 0.01), perceived high workplace related stress (p = 0.02), and history of lifetime trauma (p = 0.01) were significantly associated with greater PTSD severity after controlling other variables. This study highlights the importance of modifiable variables for reducing PTSD severity after a workplace traumatic event in transit employees.