ImportanceSelection processes for surgical training should aim to identify candidates who will become competent independent practitioners and should aspire to high standards of reliability and validity.ObjectiveTo determine the association between measured candidate factors at the time of an Irish selection and assessment outcomes in surgical training, examined via rate of progression to Higher Specialist Training (HST), attrition rates, and performance as assessed through a multimodal framework of workplace-based and simulation-based assessments.Design, Setting, and ParticipantsThis retrospective observational cohort study included data from all successful applicants to the Royal College of Surgeons in Ireland (RCSI) national Core Surgical Training (CST) program. Participants included all trainees recruited to dedicated postgraduate surgical training from 2016 to 2020. These data were analyzed from July 11, 2016, through July 10, 2022.ExposuresSelection decisions were based on a composite score that was derived from technical aptitude assessments, undergraduate academic performance, and a 4-station multiple mini-interview.Main outcomes and measuresAssessment data, attrition rates, and rates of progression to HST were recorded for each trainee. CST performance was assessed using workplace-based and simulation-based technical and nontechnical skill assessments. Potential associations between selection and assessment measures were explored using Pearson correlation, logistic regression, and multiple linear-regression analyses.ResultsData were available for 303 trainees. Composite scores were positively associated with progression to HST (odds ratio [OR], 1.09; 95% CI, 1.05-1.13). There was a weak positive correlation, ranging from 0.23 to 0.34, between scores and performance across all CST assessments. Multivariable linear regression analysis showed technical aptitude scores at application were associated with future operative performance assessment scores, both in the workplace (β = 0.31; 95% CI, 0.14-0.48) and simulated environments (β = 0.57; 95% CI, 0.33-0.81). There was evidence that the interpersonal skills interview station was associated with future performance in simulated communication skill assessments (β = 0.55; 95% CI, 0.22-0.87).Conclusions and RelevanceIn this study, performance at the time of Irish national selection, measured across technical and nontechnical domains in a multimodal fashion, was associated with future performance in the workplace and in simulated environments. Future studies will be required to explore the consequential validity of selection, including potential unintended effects of selection and ranking on candidate performance.