Delayed-onset posttraumatic stress disorder (DPTSD) has been under medico-legal debate for years. Previous studies examining the prevalence and underlying mechanisms of DPTSD have yielded inconclusive findings. This study examined the role of social resources and warzone exposure in DPTSD. Six hundred and seventy-five Israeli veterans from the 1982 Lebanon War, 369 with antecedent combat stress reaction (CSR) and 306 without CSR, were assessed prospectively, 1, 2, and 20 years after the war. Veterans were divided into 4 groups, according to the time of first PTSD onset (first onset at 1983, 1984, and 2002 and no-PTSD onset). Participants completed self-report questionnaires tapping various social resources (social network support, family environment, military company environment, homecoming reception), as well as subjective and objective warzone exposure. Our results show that a significant portion (16.5%) of the veterans reported DPTSD. As hypothesized, social resources were found to be implicated in DPTSD. Interestingly, however, social resources accounted for long—not short—delays in PTSD onset. In addition, higher levels of both objective and subjective battle exposure were associated with a more immediate PTSD onset. Finally, CSR was found to be the most powerful predictor of DPTSD. Theoretical and clinical implications of these findings are discussed.