A case is described where an otherwise fit young female patient developed;a large submasseteric abscess following the uneventful extraction of a non-infected maxillary third molar under local anaesthesia with intravenous sedation. This report highlights the difficulty of clinical diagnosis especially in the early stages of the infection. This case also demonstrates the imaging modalities used to confirm the diagnosis. It is likely that the infection in. this. case arose in an infratemporal fossa haematoma resulting from reactionary haemorrhage. Careful injection of local anaesthetic with aspiration may prevent this complication arising. This is the first reported case of a submasseteric abscess associated with,the extraction of a clinically non-infected maxillary third molar.