Ventriculitis developed suddenly in a patient with an undiagnosed abscess and was accompanied by obtundation, fever, meningismus, and hemiplegia. Aspiration of a streptococcal thalamic abscess and high doses of intravenous penicillin produced marked improvement. Increasing dysphasia 5 weeks later was accompanied by ventricular dilatation, most marked on the left, with no evidence of recurrent abscess. The left foramen of Monro was demonstrably patent. Shunting relieved the symptoms of aphasia; they recurred with one episode of malfunction of the shunt. This case lends support to the belief that parenchymal characteristics are important in hydrocephalus and demonstrates how asymmetrical ventricular dilatation can produce focal symptoms.