Precise determination and classification of left gastric vein (LGV) anatomy are helpful in planning for gastric surgery, in particular, for resection of gastric cancer. However, the anatomy of LGV is highly variable. A systematic classification of its variations is still to be proposed. We aimed to investigate the anatomical variations in LGV using CT imaging and develop a new nomenclature system. We reviewed CT images and tracked the course of LGV in 825 adults. The frequencies of common and variable LGV anatomical courses were recorded. Anatomic variations of LGV were proposed and classified into different types mainly based on its courses. The inflow sites of LGV into the portal system were also considered if common hepatic artery (CHA) or splenic artery (SA) could not be used as a frame of reference due to variations. Detailed anatomy and courses of LGV were depicted on CT images. Using CHA and SA as the frames of reference, the routes of LGV were divided into six types (i.e., PreS, RetroS, Mid, PreCH, RetroCH, and Supra). The inflow sites were classified into four types (i.e., PV, SV, PSV, and LPV). The new classification was mainly based on the courses of LGV, which was validated with MDCT in the 805 cases with an identifiable LGV, namely type I, RetroCH, 49.8 % (401/805); type II, PreS, 20.6 % (166/805); type III, Mid, 20.0 % (161/805); type IV, RetroS, 7.3 % (59/805); type V, Supra, 1.5 % (12/805); and type VI, PreCH, 0.7 % (6/805). Type VII, designated to the cases in which SA and CHA could not be used as frames of reference, was not observed in this series. Detailed depiction of the anatomy and courses of LGV on CT images allowed us to evaluate and develop a new classification and nomenclature system for the anatomical variations of LGV.