We report a 72-year-old patient presenting acute painful partial left IIIrd nerve palsy with pupillary involvement. Due to the patient's age and mild hyperlipidemia a microangiopathic ischemic origin was assumed after a compressive or inflammatory cause had been excluded by magnetic resonance imaging, blood and cerebrospinal fluid analyses. Carotid ultrasound examination disclosed a high-grade stenosis of the ipsilateral internal carotid artery (ICA). In the absence of diabetes mellitus, other significant vascular risk factors and leukoencephalopathy indicative of advanced arteriosclerotic disease, we suggest a pathogenetic role of the ICA stenosis in ischemic IIIrd nerve palsy. The frequency of a IIIrd nerve palsy as the presenting symptom in patients with ICA stenosis as well as the frequency of an ICA stenosis being the cause in patients with isolated IIIrd nerve palsy is not well documented in the literature. Both seem to be rare but may be underestimated. We advocate cervicocerebral ultrasound examination in patients presenting IIIrd nerve palsy with no obvious or a presumed ischemic cause.