Suicide-specific rumination, a repetitive mental fixation on one’s suicidal thoughts and intentions, may influence the transition from suicidal thoughts to behaviors. Research on suicide-specific rumination has been hindered by the lack of an independent measurement tool. This article presents the development and validation of a self-report measure of suicide-specific rumination across several samples with lifetime suicidal ideation (Sample 1: N = 494 students; Sample 2: N = 219 community members; Sample 3: N = 128 adults at high risk for suicide). The Suicide Rumination Scale (SRS) item pool was reduced from a pool of 41 items to 8 items that are highly discriminant and of varying levels of difficulty. The SRS demonstrated measurement invariance, convergent validity, and nonredundancy with related measures. Importantly, the SRS differentiated suicide attempters from ideators, suggesting its potential clinical relevance. Overall, these findings suggest that the SRS is a valid and incrementally useful measure of suicide-specific rumination.