STUDY DESIGN: Immunohistochemical study on fresh cadaver specimens. OBJECTIVE: Assessment of mechanoreceptor and nociceptor levels and distribution in iliolumbar ligament. SUMMARY AND BACKGROUND DATA: The function of iliolumbar ligament and its role in low back pain has not been yet fully clarified. Understanding the innervation of this ligament should provide a ground which enables formation of stronger hypotheses. METHODS: Bilateral 30 iliolumbar ligaments of 15 fresh cadavers were included in the study. Morphologic properties were recorded and the ligaments were examined by focusing on 3 main parts: ligament, bone insertions, and tendon body. Assessment of mechanoreceptor and nociceptor levels and their distribution in iliolumbar ligament were performed on the basis of immunohistochemistry using the S-100 antibody specific for nerve tissue. RESULTS: Iliac wing insertion was found to be the richest region of the ligament in terms of mechanoreceptors and nociceptors. Pacinian (type II) mechanoreceptor was determined to be the most common (66.67%) receptor followed by Ruffini (type I) (19.67%) mechanoreceptor, whereas free nerve endings (type IV) and Golgi tendon organs (type III) were found to be less common, 10.83% and 2.83%, respectively. CONCLUSION: Immunohistochemical staining has shown that iliolumbar ligament had a rich nerve tissue. Those results indicate that ILL plays an important role in proprioceptive coordination of lumbosacral region alongside its known biomechanic support function. Moreover, the presence of type IV nerve endings suggest that the injury of this ligament might contribute to the low back pain.