The lumbar plexus is situated within the substance of the posterior part of psoas major muscle. It is formed by the ventral rami of the frist three nerves  and greater part of the fourth lumbar nerve with or without a contribution from the ventral ramus of last thoracic nerve. The pattern of formation of lumbar plexus is altered if the plexus is prefixed (if the third lumbar is the lowest nerve which enters the lumbar plexus) or postfixed (if there is contribution from the 5^th lumbar nerve). The branches of the lumbar plexus may be injured during lumbar plexus block and certain surgical procedures, particularly in the lower abdominal region (appendectomy, inguinal hernia repair, iliac crest bone graft harvesting and gynecologic procedures through transverse incisions). Thus, a better knowledge of the regional anatomy and its variations is essential for preventing  the lesions of the branches of the lumbar plexus.