Numerous accessory muscles are present in the human body, many of which are clinically significant. We present a case of an anomalous accessory iliacus composed of 2 heads, whose occurrence and anatomical location indicate a high probability of causing femoral nerve compression.During a routine dissection of the posterior abdominal wall of a 78-year-old cadaver, a double-headed accessory muscle was noted, measured, and photographed.In addition to the normal anatomy of dissected structures from the posterior abdominal wall, an accessory iliacus muscle composed of superficial and deep heads was identified. In addition, the inferior roots of the divided femoral nerve located between the heads was found to follow an unusual course.It is important to be aware of morphological variability around structures such as the double-headed accessory iliacus muscle presented in this study, due to their association with neurovascular bundles and hip joints. The reported atypical morphology is not widely known in the literature but might be of great clinical significance; therefore, knowledge of such variability might be regarded in order to diagnose properly and introduce accurate treatment.