The National Biobank of Korea (NBK) is a government supported project that aims at consolidating various human-originated biomedical resources collected by individual hospitals nation-wide and integrating them with their donors' clinical information which researchers can take advantage of. In this paper, we present our experiences in developing the Clinical Information Integration System (CIIS) for NBK. The system automatically extracts clinical data from hospital information systems as much as possible to avoid errors from manual entry by human errors. It maintains the independence of individual hospitals by employing a two-layer approach, one of which takes care of all hospital-specific aspects. Interoperability is achieved by adopting HL7 v2.x messaging between the biobank and hospitals. We report the current status of the biobank and system deployments. We finally identify limitations and discuss how to improve them.