Abstract Research has demonstrated a negative association between social support and symptoms of posttraumatic stress disorder (PTSD). This has been interpreted as a protective influence of social support against the development of posttraumatic stress symptoms (PTSS). Research on the opposite association is more limited, but findings suggest that PTSS have a negative impact on social support. There is conflicting evidence that these effects are moderated by gender. Few studies have assessed both associations and gender moderation in a postdisaster context. We examined the longitudinal and bidirectional effects of emotional support and PTSS and whether gender moderates these effects among U.S. survivors of the 2017–2018 season. Participants ( N = 1,347) were assessed at four time points over 1 year. Bidirectional effects were assessed using cross‐lagged, autoregressive analyses with the combined sample (Model 1) and grouped by gender (Model 2) to assess gender moderation. The results supported small bidirectional negative effects of social support and PTSS on one another from one assessment point (e.g. Wave 1) to the subsequent point (e.g., Wave 2) for all waves, βs = −.07—.15, p < .001– p = .040. Multigroup analyses suggested the effects were not significantly different by gender. Overall, the results suggest that social support and PTSS may mutually diminish one another. Such effects may result in a positive or negative cascade wherein high PTSS may lead to lower social support and, therefore, even higher PTSS and vice versa. These findings support the importance of including social support in interventions to promote PTSS prevention and recovery.