Introduction Chylous leakage into the retroperitoneum is a rare complication after spinal surgery using an anterior retroperitoneal approach. Chylothorax is the presence of lymphatic fluid in the pleural cavity and it is even less frequent during these surgeries. The aim of this work is to report the first case of isolated left chylothorax after a retroperitoneal Left Oblique Lumbar Interbody Fusion in supine position in an adult female patient. Case A female 30-years-old patient underwent L4-L5 anterior interbody fusion. Four days after the intervention she was diagnosed with isolated left chylothorax that was drained and treated conservatively with good outcomes. Conclusion Chylothorax is an extremely rare complication after anterior lumbar spine procedures, and it is usually secondary to a chyloretroperitoneum. We present a unique case of isolated chylothorax after anterior retroperitoneal lumbar approach successfully treated in a conservative manner. Key Words chylothorax; spine; lumbosacral region; arthrodesis.