The incidence of cancer in choledochal cysts (CCs) in adults was calculated to determine the timing and need for surgery. In 78 publications (1996-2010), 434 of 5780 reported CCs patients had cancer. Cholangiocarcinoma (70.4 %) and gallbladder cancer (23.5 %) were the most common malignancies. Only nine malignancies were reported before age 18 (0.42 %). In contrast, the incidence of malignancy in adults was 11.4 %. The median age for diagnosis of cancer was 42 years, and the incidence increased with each decade.