Five diabetic patients had acute visual impairment due to papilloedema, which was bilateral in two patients. The clinical features and subsequent course were compatible with ischaemic optic mononeuropathy presumed to result from ischaemia in a posterior ciliary artery. This cause should always be considered in the differential diagnosis of papilloedema in a diabetic patient to avoid the instigation of inappropriate and invasive investigations. In general the condition has a good prognosis.