Background: Current training programs for complex pediatric minimal invasive surgery (MIS) are usually bulk training, consisting of 1- or 2-day courses. The aim of this study was to examine the effects of bulk training versus interval training on the preservation of high-complex, low-volume MIS skills. Materials and Methods: Medical students, without prior surgical experience, were randomly assigned to either a bulk or interval training program for complex MIS (congenital diaphragmatic hernia [CDH] and esophageal atresia [EA] repair). Both groups trained for 5 hours; the bulk group twice within 3 days and the interval groups five times in 3 weeks. Skills retention was assessed at 2 weeks, 6 weeks, and 6 months posttraining, using a composite score (0%-100%) based on the objective parameters tracked by SurgTrac. Results: Seventeen students completed the training sessions (bulk n = 9, interval n = 8) and were assessed accordingly. Retention of the skills for EA repair was significantly better for the interval training group than for the bulk group at 6 weeks (P = .004). However, at 6 months, both groups scored significantly worse than after the training sessions for EA repair (bulk 60 versus 67, P = .176; interval 63 versus 74, P = .028) and CDH repair (bulk 32 versus 67, P = .018; interval 47 versus 62, P = .176). Conclusion: This pilot study suggests superior retention of complex pediatric MIS skills after interval training, during a longer period of time, than bulk training. However, after 6 months, both groups scored significantly worse than after their training, indicating the need for continuous training.