The perforation of the medial acetabular wall during total hip arthroplasty due to drilling is not uncommon. But, it has rarely been associated with serious adverse events. Here, we present a case report describing an iliacus hematoma with subsequent femoral nerve palsy after primary total hip arthroplasty in a 67-year-old woman who underwent primary total hip arthroplasty due to painful hip osteoarthritis. The diagnosis was made by pelvic magnetic resonance imaging. Conservative treatment was employed and the symptoms were resolved within 3 months. It should be borne in mind that femoral nerve palsy may occur after total hip arthroplasty. It may be due to a treatable cause, such as iliacus hematoma. So, pelvic MRI is recommended in such a condition, rather than just observation.