Objective: Research findings have indicated that mothers of children diagnosed with life-threatening illnesses can be at risk for posttraumatic stress disorder (PTSD) symptoms (PTSS), with African American mothers being especially vulnerable because of evidence suggesting higher rates of PTSD among both African Americans and women. Race/ethnicity, past trauma exposure and the interaction of these variables were evaluated as risk factors for PTSS, depression, and state and trait anxiety among African American and Caucasian mothers of chronically ill children. Method: Mothers of children (N = 91) diagnosed with a life-threatening illness (i.e., cancer or Type-I diabetes mellitus [T1DM]) completed standardized measures and provided a salivary cortisol sample while attending medical appointments for their ill children. Results: A MANCOVA revealed that mothers of children diagnosed with T1DM had higher cortisol levels than mothers of children with cancer. There was no racial or ethnic disparity in the risk of PTSS among the mothers. Conclusion: These findings suggest that mothers of children with T1DM may be vulnerable to stress reactions, as reflected by cortisol, a biological marker. Clinicians and researchers might consider illness-specific features when evaluating the risk of stress reactions among mothers of children with life-threatening illnesses.