Intracranial empyemas are collections of pus, which usually develop in the subdural or extradural space; the former is more frequent. They are not common lesions, forming about one fifth to one third of reported series of intracranial abscesses [1, 2]. In the preantibiotic era, they were commonly fatal [3], but a review of series reported since widespread use of antibiotics indicated a continuing mortality rate of 25% [4]. Their radiological interest resides not only in their importance, but also in the problems of early diagnosis. Negative results have been reported with a number of techniques, including radionuclide imaging [5], computed tomography (CT) [2, 4, 6, 7] and cerebral angiography [8, 9]. A recent neurosurgical review concluded balefully that “no reassurance can be obtained from negative investigations”. The present study is an examination of the possible ways in which such negative studies, particularly CT, can be avoided.