Recently, it becomes conspicuous that the network should have enough communication bandwidth and be organized with steadiness to operate and support hospital information system successfully. Seoul National University Hospital completed to reconstruct legacy network which had been used since 1995. We had a consultation to diagnose the current problems and reconstructed the network according to the consultation. The design of network architecture was mainly focused on the circuit route in case of error condition and the suitable bandwidth for the easy communication. We also regulated the use of unsuitable protocols which might broadcast inappropriate data packets over the whole network. After 6 months of operation we evaluated the performance of newly constructed network. The average traffic rate from the input port of main servers was 0.5% and that from the output port was 6% separately. The average traffic rate on the overall ATM backbone showed around 1 %.From the result, we concluded that the newly constructed network had such an enough capability supporting hospital information system without any interruption. Furthermore, we expect that it will be sufficient to support the additional traffic increment by PACS and group ware applications.