Alexithymia, psychological distress, and posttraumatic stress disorder (PTSD) are highly related constructs. The ongoing debate about the nature and relationship between these constructs is perpetuated by an overreliance on cross-sectional research. We examined the longitudinal interactive relationship between alexithymia, psychological distress, and PTSD. We hypothesised that there is an interactive relationship between the three constructs. Military personnel (N = 1871) completed the Toronto Alexithymia Scale, the Kessler 10 and a PTSD Checklist (PCL-C) at pre-deployment, post-deployment, and at 3–4 years following (...) the post-deployment assessment. We initially tested whether psychological distress is either a moderator or mediator in the relationship between alexithymia and PTSD across the time points. General psychological distress was a partial mediator of total PTSD severity and hyperarousal symptomology at all three time points. Psychological distress fully mediated re-experiencing and avoidance symptomology at all three time points. Our results suggest that those with alexithymia are at longitudinal risk of developing more severe PTSD symptomology and experiencing hyperarousal irrespective of temporal proximity to traumatic exposure. Further, vulnerability to the emergence of re-experiencing and avoidance symptomology for those with alexithymia is increased when one experiences greater distress. Our results show that alexithymia is a persistent risk factor for PTSD symptomology. (shrink)