This disease card provides information on the epizootic of koi and common carp in Indonesia. The pattern of the recent epidemic in koi and common carp in Indonesia is consistent with that of an infectious disease, but there is as yet no definitive aetiological diagnosis. The Regional Aquatic Animal Health Advisory Group of NACA in its first meeting (November 2002) decided to list Koi mass mortality under Unknown diseases of serious nature in the Quarterly Aquatic Animal Disease (QAAD) report, to assist in the collation of data from the Asia-Pacific region starting in 2003.