The after-hours effect on postoperative complications has been poorly studied in the neurosurgical literature. A recent retrospective analysis showed that patients with a surgical start time (SST) between 09:01 pm and 07:00 am had a greater risk of complications. This study used a prospective registry to examine the relationship between SST and postoperative complications in a large neurosurgical population. We performed a prospective longitudinal cohort analysis of all consecutive adult patients admitted to our neurosurgery service between October 1, 2018 and May 1, 2019. Complications were prospectively recorded and classified as surgical or medical. Univariate and multivariate logistic regressions were used to analyze these data. Eighty-five surgical complications (6.6%) and 110 medical complications (8.6%) resulted from 1285 operations on 1145 patients. Later SST was predictive of complications in the emergent population (odds ratio [OR], 2.28; 95% confidence interval [CI], 1.01-5.15; P= 0.048) but not in the elective population. Extubation in the neurosurgical intensive care unit (NICU) versus the operating room strongly predicted medical complications (OR, 6.91; 95% CI, 3.33-14.34; P < 0.0001). Patients with a later SST were significantly more likely to be extubated in the NICU (P < 0.0001). Patients undergoing emergent operations with a later SST were significantly more likely to have a postoperative complication. Patients who were extubated in the NICU versus the operating room were significantly more likely to have a medical complication. Patients were more likely to be extubated in the NICU if they had a later SST; therefore, SST may indirectly be associated with an increase in medical complications.