This study aims to determine the level of origin, branching pattern and exits of the iliohypogastric and ilioinguinal nerves in relation to the psoas major muscle. Additionally, this study confirms the presence and retroperitoneal courses of the double nerves. We dissected a total of 24 iliohypogastric and ilioinguinal nerves (6 male and 6 female cadavers). The origin, branching, and exits in relation to the psoas major muscle, the absence of these nerves or the presence of double nerves, and their retroperitoneal course were carefully examined. All the images were recorded by photographing. In this study, we mainly observed variations in exits, branching patterns, and their retroperitoneal course. The iliohypogastric nerve was absent in 2 cases (8.3%). In the type I pattern, in 1 case (4.2%), the common trunk descends anteriorly to the iliac vessels from the iliolumbar vessels. In 4 cases (16.7%), the double ilioinguinal nerve with different branch patterns and retroperitoneal courses was observed. In 1 single nerve case (4.2%), the ilioinguinal nerve descends anterior to the iliac vessels from the iliolumbar vessels. To our knowledge, the branching pattern of the double ilioinguinal nerves and their retroperitoneal course have not been reported in any available data. Sound knowledge of the variations in the origin, branches, and retroperitoneal course of the iliohypogastric and ilioinguinal nerves is very helpful for the improvement of peripheral nerve blocks and other various surgical procedures to avoid complications and nerve injuries.