Most individuals who die by suicide have contact with a physician in the year before their death. There are no randomized trials that have evaluated suicide intervention training for medical students or physicians. The objective of this study was to determine the effectiveness of a gatekeeper training program on suicide intervention behavior using Objective Structured Clinical Examinations (OSCEs) in medical students. A randomized controlled trial design was used. Participants were 112 undergraduate medical students at the University of Manitoba. The 2-day Applied Suicide Intervention Skills Training (ASIST) program was completed by half of the participants, according to a stratified block randomization design. Scores on OSCEs and scores on the Suicide Intervention Response Inventory (SIRI-2) were used as objective measures of intervention behaviors. There was a a significant Group-by-Time interaction on OSCE data, demonstrating that medical students who received ASIST performed significantly better than medical students who received training as usual (p<.001). The two groups did not differ significantly from each other on the SIRI-2 (p=.78). ASIST training improved the ability of medical students to detect and intervene with a standardized suicidal patient as assessed by OSCEs, compared to medical school training as usual. This study provides support for ASIST training for medical students to develop skills in recognition and management of suicidal patients.