A comprehensive clinical and neuropsychological study was made of 34 patients with thalamic arteriovenous malformations. In the thalamus. Memory disorders were a common abnormality (in 31 of 34 patients). They were modally nonspecific and depended on the site of arteriovenous malformations. With the prevalent ventricular pattern of hemorrhages, memory disorders were accompanied by disorientation and emotional and volitional impairments. Arteriovenous malformation was removed in 12 patients (on the left side in 7 patients and on the right in 5). After surgery there was virtually progression of memory defects in all patients. Speech disorders combining the specific features of lesions in various cortical regions were detected in 5 of 7 patients with left thalamic arteriovenous malformations.