The contribution of computed tomography (CT) in the assessment of macrocrania has been examined with reference to a consecutive series of 93 cases. In the great majority a definitive diagnosis could be made without resorting to more noxious procedures. Hydrocephalus was present in 46% of this group. The incidence of macrocrania with childhood hydrocephalus and its relationship to the aetiology and other CT features was examined with reference to 109 consecutive cases with hydrocephalus shown on CT. Macrocrania was present in only 11% of cases with an underlying tumour, but in 71% with other obstructing lesions.