Objectives This prospective study aims to assess the role of fathers' posttraumatic stress disorder (PTSD) symptoms (PTSS), the course of these symptoms over the years, and the relationship between these symptoms and their adult offspring's own PTSS and level of differentiation of self. Method A sample of 123 Israeli father–child dyads (79 ex‐prisoners of war [ex‐POWs] dyads and a comparison group of 44 veterans' dyads) completed self‐report measures. The fathers participated in 2 waves of measurements (1991 and 2008), while the offspring took part in 2013–2014. Results Increase in the fathers' PTSS over the years was related to high levels of his offspring's PTSS. Among ex‐POWs' offspring, self‐differentiation mediated the association between the father's PTSS and offspring's PTSS. Thus, a greater increase in the ex‐POWs' PTSS over time was correlated to lower levels of the offspring's self‐differentiation, which in turn was correlated to higher rates of PTSS. Conclusion Veterans' PTSS as well as offspring's self‐differentiation are mechanisms of the intergenerational transmission of captivity trauma.