The current outbreak of avian influenza H5N1 began in South-east Asia in 2003 and by 6 February 2007 had caused outbreaks in birds in 53 countries resulting in the deaths of 166 humans, and 200 million poultry (the latter mostly culled under disease control measures). H5N1 rarely infects humans but is a highly infectious fatal disease of poultry with an unknown epidemiology in zoo bird species. Concern about the potential for this virus to mutate and create a human pandemic has fuelled public concern. The spread of the disease around the world has been attributed to migratory birds and poultry movements. Bird vaccination for zoo collections is available in some countries although its effectiveness in many zoo species is as yet unknown. Protection of zoo stock should therefore be based upon strict biosecurity balanced against the welfare of the birds. The future of vaccinated birds is not certain; they may not be permitted to be released to the wild and some countries may ban their entry resulting in a detrimental effect on the future of captive-breeding and release programmes. This paper reviews the recent history of the epidemic and some of the issues that this disease raises for zoological collections.