The blood vessels of the insular cortex and the claustrum were studied in 26 foetal brains of 16--25-week-old foetuses and one adult brain without noticeable pathological signs. The labelling of the vessels was wade according to Duvernoy et al. (1981). In 16-week-old foetuses arteries of types A6 as the A5 were found in the insular cortex as well as the veins of type V5. In 19-week-old foetuses the arteries of type A4 and the veins of type V4 appeared as only cortical vessels. In the following stages of the brain development the shorter and shorter arteries appeared so that in 24-week-old foetuses one could see all the types of arteries from A6 to A1. However, in the period from 19 to 25 weeks, no vein shorter than that of the type V4 was found in the insular cortex. In the adult brain it was possible to identify all the types of arteries and veins in the insular cortex, but distances between the individual vessels were larger in comparison with those in the insular cortex of the foetal brains. There claustrum was vascularized by the arterial branches from the insular arteries, whereas in the adult brain the claustrum received some of the branches from the striate arteries as well. This pattern of the vascular supply may indicate the common origin of the claustrum and the insular cortex.