Despite considerable speculation among terrorism researchers regarding the conditions leading to organizational desistance from terrorism, quantitative analysis of terrorism frequently focuses on terrorist attacks as the unit of analysis, resulting in a near complete absence of analyses of terrorist organizations themselves. Moreover, research on organizations that engage in terrorism has generally been limited to case studies of individual organizations. Toward a more general understanding of what conditions predict organizational desistance from terrorism, this study uses newly available data from the Global Terrorism Database to analyze the terrorist activity of 557 organizations that were active for at least 365 days between 1970 and 2008. Much like research on conventional crime, prior research on terrorism has focused almost exclusively on the onset of criminal behavior and has neglected determinants of declining activity. Here I use group-based trajectory models to investigate patterns of decline in organization-level terrorist activity. In particular I examine how patterns of onset relate to patterns of decline among these organizations. I first estimate the trajectory models for the organizations’ frequency of attacks, and then calculate the annual ratio of attacks to attacks-at-peak for each organization in order to isolate patterns of decline, independent of the magnitude of activity. I then repeat the trajectory analysis to determine if the relative shape of the organizational trajectory has significance beyond the overall frequency of attacks. I find that the speed and magnitude of an organization’s emergence are correlated with its longevity such that those organizations characterized by rapid onset are two to three times more likely than those characterized by moderate onset to reach moderate or high levels of attacks per year. Likewise, as the rate and overall volume of attacks at onset increase, so does the likelihood that the group will follow a persistent pattern of decline. I conclude with a discussion of the implications of patterns of decline among terrorist organizations for research and policy.