This study investigated circulating natural killer (NK), CD4+ and CD8+ cells in response to acute psychological challenge among mothers of child cancer survivors with and without posttraumatic stress symptoms (PTSS). Control mothers of healthy children (n = 9) were compared to 17 cancer mothers with (PTSS: n = 9) and without PTSS (No PTSS: n = 7) under conditions of rest, after a generic stressor (MAT: mental arithmetic task) and a personalized stressor (script-driven trauma imagery), and after recovery from each stressor. Results indicate the PTSS group had higher percentage CD4+ and lower CD8+ levels than non-symptomatic women and blunted NK reactivity to generic challenge. Multiple regression analyses indicated PTSS effects were independent of selfreported distress. Contrary to expectations, cancer mothers without PTSS were not significantly different from controls on tonic or phasic immune outcomes. Also unlike predictions, reactivity to challenge was greatest to the non-social MAT stressor compared to the personalized challenge for all groups. Conclusions are constrained by study limitations (e.g., small sample size and potential phase order effects). Nonetheless, results are consistent with an emerging literature on PTSSassociated immune differences and further suggest these effects may be distinct from that associated with subjective distress more generally.