The purpose of this study was to assess how attendance at a peer-led sexual harassment workshop affects college students' intervention in response to their peers' sexually harassing behaviors. A quasi-experimental panel design was used to assess change over an interval of six months. An instrument, the Sexually Harassing Behaviors Bystander Intervention Inventory (SHBBII), was developed to measure self-reported intervention response to different sexually harassing behaviors. College student peer sexually harassing behaviors were categorized as gender harassing, taunting or intrusive sexually harassing behaviors. Statistically significant differences were found between control and workshop students' post-test interventions on Gender Intervention, Intrusive Intervention and Total Intervention scores. Students intervened more as observers among other witnesses than when they were sole witnesses. A causal model was constructed from a blocked hierarchical regression analysis for each of the sexually harassing behavior dimensions and for Total Interventions, using five student characteristics (student gender, academic class, racial/ethnic identity, resident assistant status and other sexual harassment training experience), pre-test scores and treatment condition. Implications for program assessment, educational policy, future legal directions and future research are discussed.