Inclusion Criteria:  Retrospectively review PSC cases before April 1, 2002 will be identified by diagnostic codes from the International Classification of Diseases (ICD)-9, and for those after April 1, 2002, we used ICD-10. We identified patients using an electronic search of SuValue Research Database and HIS of BFH-CMU and BYH-CMU using PSC related ICD codes (ICD-9: 576.1; ICD-10: K83.016/K83.016(China version)). To supplement the ICD search, an electronic keyword search for "primary sclerosing cholangitis" or "seclerosing cholangitis" was conducted on all radiology, endoscopy, pathology reports beginning on earliest date available in the database of SuValue Research Database and HIS of BFH-CMU and BYH-CMU. We reviewed the medical charts of identified patients and diagnostic criteria including cholestatic biochemistry (ALP, GGT elevations), and typical imaging (MRCP or ERCP) or pathological features, excluding other known etiology. For patients with multiple visits for PSC, we reviewed only the index visit. To ensure consistency, chart review was independently assessed by two hepatologists. Discrepancies in compliance were resolved by discussion between the two main reviewers. Any unresolved discrepancies were decided by a third expert hepatologist.  Exclusion Criteria:  The cases with secondary sclerosing cholangitis caused by cholelithiasis, IgG4 related disease, malignancy or other known etiologies. The cases with missing key results on clinical, biochemical (ALP, GGT, bilirubin), radiological (MRCP or ERCP) or histological investigations.