Mucocoeles of the maxillary antrum extensive enough to cause local bone destruction appear to be extremely rare. Such a case is reported with the appropriate pathological and radiological findings. Perusal of the literature suggests that this condition, unlike mucocoeles arising in other sinuses, may closely mimic a carcinoma and all authors stress the necessity for Caldwell-Luc surgery to be certain of the diagnosis. Som and Shugar (1980) describe features visible on CT scanning which may help to differentiate between mucocoeles, pyocoeles and carcinomata. In spite of the relatively high incidence of cysts of the antrum, it is thought unlikely that mucocoeles in this location would arise from such a cyst; indeed it is likely that all mucocoeles arise from blockage of the outflow tract of the appropriate sinus. There is a high incidence of maxillary sinus mucocoele in Japan following Caldwell-Luc surgery (Hasegawa et al., 1979). Noyek and Zizmor (1976) suggest that compartmentalization of the antrum after operation may leave islands of mucosa without drainage; such a collection may give rise to a mucocoele.