IMPORTANCE: In patients with intrahepatic cholangiocarcinoma (ICC), the oncologic benefit of surgery and perioperative outcomes for large multifocal tumors or tumors with contiguous organ involvement remain to be defined. OBJECTIVES: To develop and externally validate a simplified prognostic score for ICC and to determine perioperative outcomes for large multifocal ICCs or tumors with contiguous organ involvement. DESIGN, SETTING, AND PARTICIPANTS: This study of a contemporary cohort merged data from the California Cancer Registry (January 1, 2004, through December 31, 2011) and the Office of Statewide Health Planning and Development inpatient database. Clinicopathologic variables were compared between tumors that were intrahepatic, small (<7 cm), and solitary (ISS) and those that had extrahepatic extension and were large (≥7 cm) and multifocal (ELM). External validation of the prognostic model was performed using an independent data set from the National Cancer Institute’s Surveillance, Epidemiology, and End Results database from January 1, 2004, through December 31, 2013. MAIN OUTCOMES AND MEASURES: Patient overall survival after hepatectomy. RESULTS: A total of 275 patients (123 men 44.7% and 152 women 55.3%; median interquartile range age, 65 55-72 years) met the inclusion criteria. No significant differences in overall complication rate (ISS, 48 34.5%; ELM, 37 27.2%; P = .19) and mortality rate (ISS, 10 7.2%; ELM, 6 4.4%; P = .32) were found. A multivariate Cox proportional hazards model demonstrated that multifocality, extrahepatic extension, grade, node positivity, and age greater than 60 years are independently associated with worse overall survival. These variables were used to develop the MEGNA prognostic score. The prognostic separation/discrimination index was improved with the MEGNA prognostic score (0.21; 95% CI, 0.11-0.33) compared with the staging systems of the American Joint Committee on Cancer sixth (0.17; 95% CI, 0.09-0.29) and seventh (0.18; 95% CI, 0.08-0.30) editions. CONCLUSIONS AND RELEVANCE: The MEGNA prognostic score allows more accurate and superior estimation of patient survival after hepatectomy compared with current staging systems.