Language disorders developed in a patient following a subcortical infarct involving the left putamen and caudate nucleus. Language was abundant and fluent, with many perseverations, semantic and ideation incoherences, and all activities concerned with verbal or non-verbal expression were affected. Lesions were present in the head and body of the caudate nucleus, the whole of the putamen, the anterior nucleus of the thalamus and the superior part of the internal capsule. The disorder was unique in relation to disturbances of the aphasic type observed in extensive thalamic lesions, or in transcortical sensorial aphasia. Physiopathological interpretation is based on the functional role of the putamen-caudate system in the regulation of many types of behaviour: animal experiments and results of applying stimuli in humans suggests a release of the inhibition exerted by the caudate nucleus on the frontal cortex. Lack of comparable clinicopathological data implies that other similar cases must be reported before the specificity of the disorder can be confirmed.