The arterial supply to the left hemiliver was studied in 70 liver casts. The arteries were divided into 15 groups according to their origin and branching pattern. The left hemiliver was supplied by one artery in 53% of cases, by two arteries in 40% and by three arteries in 7%. The left hepatic artery, which originated from the proper hepatic artery, supplied all three left segments in 39% of specimens. The replacing left hepatic artery, which originated from the left gastric artery, supplied the whole left hemiliver in 3% of cases. The incomplete, replacing left hepatic artery supplied segments 2, 3 and a part of segment 4 in 6% of cases, and only segments 2 and 3 in 11%. There was one segmental artery for segment 2 in 86%, and two in 14%. Segment 3 was supplied by one artery in 87%, and by two in 13%. Segment 4 was supplied by one artery in 39% of cases, by two arteries in 43%, by three in 14% and by four arteries in 4%.