Symptoms of damage in coconut (Cocoa nucifera L.) caused by the eriophyid mite Aceria guerreronis Keifer are described. The pest outbreak was first observed in Kerala state in 1997 and within a period of two years it has spread to almost all the major coconut growing districts in Tamil Nadu. Coconut palms of 15 to 25 years age are damaged very severely (70%) by the mite. When buttons of three to four months old are affected, yield loss in terms of copra output is as high as 40 per cent. Green coloured nuts are more susceptible than orange or yellow coloured nuts. The percent damage by mite is less in pesticide treated trees when compared to untreated trees. The varieties Lakshadweep Ordinary, Cochin China, Andaman Ordinary and Gangabondam recorded less than 13 per cent damage by the mite. Keywords: Coconut, eriophyid mite, Aceria guerreronis.