Early interventions that reduce the societal burden of mental health problems in the aftermath of disasters and mass violence have the potential to be enormously valuable. Internet-based interventions can be delivered widely, efficiently, and at low cost and as such are of particular interest. We describe the development and feasibility analysis of an Internet-delivered intervention designed to address mental health and substance-related reactions in disaster-affected populations. Participants (n = 285) were recruited from a cohort of New York City-area residents that had been followed longitudinally in epidemiological research initiated 6 months after the terrorist attacks of September 11, 2001. The intervention consisted of 7 modules: posttraumatic stress/panic, depression, generalized anxiety, alcohol use, marijuana use, drug use, and cigarette use. Feasibility data were promising and suggest the need for further evaluation.