Yonsei University Medical Center (YUMC) in Seoul, Korea is 114 years old and 1,582 beds in Shinchon Severance hospital in main university campus and 746 beds in affiliated Youngdong Severance hospital which is 20 miles away from the main campus. The dental hospital in main campus is also included in a full-PACS system. The numbers of exams/year for main, affiliated, and dental hospitals are approximately 558,000, 365,000, and 181,000, respectively. Since 1997, a Mini-PACS with 3xMRI, 2xDSI, and 2xCT in Shinchon Severance hospital has been operating to archive the digital data and to view them with DICOM viewer PiViewTM. An archiving system with 2xCT and 2xMRI in Youngdong Severance has been operating to archive the digital data. We are now designing a large-scale full-PACS for YUMC with experiences of running a mini-PACS for 3 years. The 11xUS, 7xEndoscopy, 7xCR, 3xSPECT, 1xPET, 1xCT simulator, and digital camera based patient database in the Dept. of radiation oncology in Shinchon Severance hospital will be connected to an archiving server system through modality interface gateway. The 3xCR, 2xDSA, 2xFD, 5xUS, 3xEndoscopy in Youngdong Severance hospital will be connected to the main archiving system. The 1xCT, 10xIntraoral X-ray unit DR, 4xPanoramic&cephalometric unit DR, 1xTranscranial CR, 1xScanora X-ray unit CR, 1xSectography CR in dental hospital will be connected to archiving server system through modality interface gateway. The estimated amount of data for Shinchon severance, Youngdong severance, and dental hospitals per year are 11.55TB, 5.88TB, and 0.96TB, respectively. The current mini-PACS server includes 54 GB RAID, 520 GB DLT with SUN SpectraTM server. The main server in Shinchon Severance hospital needs to be upgraded to 600GB RAID for 30 days and 10TB ODJ or DLT for the first two years. Youngdong Severance hospital needs to be installed a main server with 600GB RAID for > 30 days and 10TB ODJ or DLT for > 2 years. The interface between HIS/RIS and PACS needs to be developed using a PACS broker. YUMC has successfully been operating the Mini- PACS for last 3 years and now expanding to a full-PACS for 558,000 exams/year in Shinchon Severance, 365,000 exams/year in affiliated Youngdong Severance, and 181,000 exams/year in dental hospitals.