Bonamiasis, caused by Bonamia ostreae, was confirmed in native flat oysters Ostrea edulis L. in England in 1982. Hudson & Hill (1991; Aquaculture 93:279-285) documented investigations into the initial spread of the disease in wild and cultivated stocks of native oysters in the UK. They also described the controls that were initially applied to prevent the further spread of the pathogen. This paper reports on subsequent controls and associated monitoring applied in the UK and reports on the epidemiology of the disease in the 30 yr from 1982 to 2012. Bonamiasis remained confined to the zones in England as documented by Hudson & Hill (1991) until 2005, when it was confirmed in Lough Foyle, Northern Ireland. In 2006 it was found in 2 new areas, one in Wales and one in Scotland. Subsequent further spread to additional areas in all parts of the UK has resulted in 9 zones being currently designated as infected with the disease. In addition, a single oyster from one area has tested positive for the closely related B. exitiosa. In general, analysis of the results of the monitoring programme in England and Wales shows no clear trend in infection levels over time, although there has been an apparent decrease in the level of infection in some fishery areas. In an autumn sampling programme the highest levels of infection were detected in October.