Aims.: To investigate whether adverse childhood experiences (ACEs) modify the impact of exposure to a natural disaster (the 2011 Great East Japan earthquake and tsunami) on the occurrence of posttraumatic stress disorder (PTSD) among older people. Methods.: Data were collected as part of the Japan Gerontological Evaluation Study (JAGES), which is an on-going epidemiological survey investigating social determinants of health among older people across Japan. Information on PTSD symptoms based on the Screening Questionnaire for Disaster Mental Health, traumatic exposure to the earthquake (i.e., house damage and loss of relatives/friends during the earthquake/tsunami) and ACEs was obtained from 580 participants aged 65 or older living in Iwanuma City, Miyagi Prefecture, which suffered severe damage as a result of the earthquake and the subsequent tsunami in March 2011. Associations were examined using Poisson regression analysis with a robust variance estimator after adjusting for covariates. Results.: The prevalence of PTSD was 9.7% in this population; compared to those with no traumatic experience, the prevalence of PTSD was approximately two times higher among those who experienced the loss of close friends/relatives (PR = 1.84, 95% CI = 1.11–3.03, p = 0.018), or whose house was damaged (PR = 2.15, 95% CI = 1.07–4.34, p = 0.032). ACE was not significantly associated with PTSD. Stratified analyses by the presence of ACE showed that damage due to the earthquake/tsunami was associated with PTSD only among those without ACEs; more specifically, among non-ACE respondents the PR of PTSD associated with house damage was 6.67 (95% CI = 1.66–26.80), while for the loss of a relative or a close friend it was 3.56 (95% CI = 1.18–10.75). In contrast, no statistically significant associations were observed among those with ACEs. Conclusion.: Following the Great East Japan earthquake/tsunami in 2011 a higher risk of developing PTSD symptoms was observed in 2013 especially among older individuals without ACEs. This suggests that ACEs might affect how individuals respond to subsequent traumatic events later in life.