Purpose: Minimally invasive surgery (MIS) is the optimal treatment for congenital biliary dilatation (CBD), but few studies on adults have been reported. We compared the postoperative outcomes of MIS with those of open surgery (OS) in adult patients with CBD. Methods: The subjects of this retrospective study were 36 adult patients who underwent surgery for CBD. We compared the postoperative outcomes of 20 patients who underwent laparoscopic (n = 15) or robotic (n = 5) surgery with those of 16 patients who underwent OS. Results: MIS was associated with a significantly higher rate of type I (p < 0.001), significantly less blood loss (p < 0.001), a significantly lower rate of internal stents (p = 0.048), significantly longer operation times (p = 0.009), and a significantly shorter postoperative hospital stay (p = 0.007) than OS. The postoperative outcomes of MIS for type I CBD were similar to those of the whole cohort. There were no significant differences in late complications between the groups. The robotic procedure had a significantly shorter operative time than laparoscopic surgery for hepaticojejunostomy (HJ; p = 0.029). Conclusions: MIS achieved favorable short-term outcomes without compromising mid-term outcomes compared to OS and is appropriate for adult patients with CBD. Robotic HJ may be more ideal than its laparoscopic counterpart.