Introduction: Neurosurgical residency training is costly, with expenses largely borne by the academic institutions that train residents. One expense is increased operative duration, which leads to poorer patient outcomes. Although other studies have assessed the effect of one resident assisting, none have investigated two residents; thus, we sought to investigate if two residents versus one scrubbed-in impacted operative time, estimated blood loss (EBL), and length-of-stay (LOS).Methods: In this retrospective review of patients who underwent a neurosurgical procedure involving one or two residents between January 2013 and April 2016, we performed multivariable linear regression to determine if there was an association between resident participation and case length, operating room time, EBL, and LOS. We also included patient demographics, attending surgeon, day of the week, start time, pre-operative LOS, procedure performed, and other variables in our model. Only procedures performed at least 40 times during the study period were analyzed.Results: Of 860 procedures that met study criteria, 492 operations were one of six procedures performed at least 40 times, which were anterior cervical discectomy and fusion, cerebrospinal fluid (CSF) shunt insertion, CSF shunt revision, lumbar laminectomy, intracranial hematoma evacuation, and non-skull base, supratentorial parenchymal brain tumor resection. An additional resident was associated with a 35.1-min decrease (p = .01) in operative duration for lumbar laminectomies. However, for intracranial hematoma evacuations, an extra resident was associated with a 24.1 min increase (p = .03) in procedural length. There were no significant differences observed in the other four surgeries.Conclusion: An additional resident may lengthen duration of intracranial hematoma evacuations. However, two residents scrubbed-in were associated with decreased lumbar laminectomy duration. Overall, an extra resident does not increase procedural duration, total operating room utilization, EBL, or post-operative LOS. Allowing two residents to scrub in may be a safe and cost-effective method of educating neurosurgical residents.