The clinicopathological findings in a patient who presented a severe frontal syndrome and who had ischaemic lesions in the left anterior cingulate gyrus and in the head of the right caudate nucleus are reported. The clinical features included complex disorders such as distractibility, docility, emotional unconcern, manual grasping, prehension and utilization behaviour, perseverations and anterograde amnesia. They are closely similar to those previously described in a patient with bilateral lesions involving the anterior cingulate gyri. These findings suggest that (i) in the presence of a lesion of the anterior cingulate gyrus on one side, a lesion of the head of the contralateral caudate nucleus may be equivalent to a lesion of the anterior cingulate gyrus, the anterior cingulate gyrus--caudate complex working as a single functional unit; (ii) the anterior cingulate gyri (and anterior cingulate gyrus--caudate complexes) play a crucial role in the expression of frontal lobe functions; (iii) they are necessary for sustained goal-oriented responses to (emotionally or not) discriminated stimuli.