To describe a large clinical series of pure laparoscopic radical nephrectomy (LRN) for left renal cell carcinoma (RCC) with differential extensions of level I renal vein (RV) tumor thrombus using a retroperitoneal approach. Ten left RCC patients with RV tumor thrombus underwent pure retroperitoneal LRN. Operation procedures were different for patients with varying length of the RV tumor thrombus. Based on our experience, four grades were defined based on the distal limit of the thrombus. Grade 1: tip of the thrombus was located between the renal sinus and the left gonadal vein (or adrenal vein); Grade 2: tip of the thrombus was located between the left gonadal vein and the abdominal aorta; Grade 3: tip of the thrombus was riding on the abdominal aorta; Grade 4: tip of the thrombus was located in the interaortocaval region. According to this classification, grade 1 in 3 patients, grade 2 in 2, grade 3 in 3, and grade 4 in 2. Pure retroperitoneal LRN and thrombectomy were successfully performed for all the patients without requiring open surgery. The mean tumor size for each of the four grades was 5.9, 6.4, 5.8, and 7.6 cm, respectively; the mean thrombus length was 2.1, 3.5, 5.2, and 7.1 cm, respectively; the mean operative time was 85, 103, 137, and 190 minutes, respectively; the average surgical bleeding volume was 67, 110, 143, and 225 mL, respectively. Better procedures are needed to increase the working space for patients with higher grades of thrombus. Surgical margins were negative for all patients. With a mean follow-up of 29 months, two patients developed metastatic disease. Despite the technical challenges, pure retroperitoneal LRN for left RCC patients with differential extensions of RV tumor thrombus is safe and feasible in selected patients. However, it is important to note that surgery will be more difficult for patients with higher grades of thrombus.