Clinical and neuroendocrinological studies were performed in 41 patients with arteriovenous malformations (AVM) of the cingulate gyrus. Before surgery, the primary affliction in 38 patients consisted of memory disturbance, 5 of these having signs of Korsakov's syndrome. Autonomic and epileptic fits were not typical. Of 38 patients undergoing surgery, postoperative worsening of memory occurred in 23, but no qualitatively new disturbances appeared. Korsakov's syndrome appeared de novo after surgery in 3 patients. The extent of memory disturbances correlated with the extent of lesions to the cingulate gyrus and with the extent to which AVM affected the corpus callosum. Qualitative analysis of memory loss syndromes revealed alterations in trace selectivity in nearly all patients and failure to retain the meaning of stories, which was accompanied by lack of insight into the patients' abnormalities. The signs of these syndromes showed clear similarity with memory deficiencies in patients with frontal lesions. This suggests that not only the frontal lobes themselves, but also their connections, are involved in producing the clinical picture in humans.