The incidence of unexplained mortalities among marine finfish in the Philippines has been increasingly observed. Considering that outbreaks of viral infections affecting similarly cultured marine fishes such as grouper and seabass were reported in many countries, a comprehensive diagnostic program to meet the challenge was initiated at the Aquaculture Department, Southeast Asian Fisheries Development Center (SEAFDEC-AQD)with funding from the Japanese Trust Fund Fish Disease Project. This activity was further boosted by the Japan International Research Center for Agricultural Sciences (JIRCAS). Overall, the program involved the staff of the marine finfish hatchery and the Fish Health Section. Cases of unexplained mortalities observed in the hatchery were referred to the Fish Health Section. Detailed information on the culture histories of each case were provided by the hatchery staff. Diagnostic tests were performed on each case and those with potential indication of viral etiology were processed for virus detection. Presumptive diagnosis of viral infections was based on typical signs, cell culture isolation histopathology and in-vivo pathogenicity tests. Confirmatory tests to identify specific viruses include RT-PCR, FAT and electron microscopy. The highlights of outbreaks of viral nervous necrosis and other virus-associated infections among marine finfish at SEAFDEC-AQD are presented.