Cognitive processes in the aftermath of experiencing a major life stressor play an important role in the impact of the event on the person. Intrusive thoughts about the event are likely to be associated with continued distress, while deliberate rumination, aimed at understanding and problem-solving, should be predictive of posttraumatic growth (PTG). The Event Related Rumination Inventory (ERRI), designed to measure these two styles of rumination, is described and validation information is provided. Using a college student sample screened for having experienced highly stressful life events, data were obtained (N=323) to conduct an exploratory factor analysis that supported the two factors of the ERRI. Separate confirmatory factor analyses (CFA) on two additional samples (Ns=186 and 400) supported a two-factor model. The two ERRI factors were validated by comparison with related variables and by assessing their contributions to predicting distress and PTG in two samples (Ns=198 and 202) that had been combined to conduct the second CFA. Data indicate the ERRI has solid psychometric properties, captures variance not measured by stable differences in cognitive styles, and the separate factors are related to posttraumatic distress and growth as predicted by existing models of PTG.