Cis AB blood group is a rare variant of the AB blood group resulting from i
nheritance of both A and B genes on one chromosome. It may lead to misclass
ification in ABO grouping and clinical misdiagnosis as a result of its dive
rgence from the laws of Landsteiner and Mendel. We encountered a case of ci
s AB blood group, and we found that autotransfusion was useful during surge
ry in this patient with a rare blood group.