The clinical symptoms comprising piriformis syndrome emerge as a result of the compression of the sciatic nerve due to anatomical variations or pathological conditions related to the piriformis muscle. The underlying cause in 6% of cases of lumbar pain, piriformis syndrome might be also defined as entrapment neuropathy of the sciatic nerve. While piriformis syndrome is not rare, it is not well known. As the clinical symptoms may be misleading, it can easily be overlooked, or lead the clinician to an incorrect diagnosis (such as discopathy). In this report, our objective was to present the case of a 18-year-old female patient who presented to the emergency department with sciatalgia and received a diagnosis of piriformis syndrome caused by pyomyositis of the piriformis muscle. The patient arrived at the emergency department reporting severe pain and paresthesia in the right pelvis, thigh, and leg with the inability to walk due to pain. Vital signs were normal except for a high fever. Her Lasègue test was positive, and the patient had severe pain with both internal and external rotation. After radiological examination, the patient was diagnosed with an abscess in the piriformis muscle due to pyomyositis. It was determined that the cause of sciatalgia was piriformis syndrome, with the abscess in the piriformis muscle compressing the sciatic nerve. The abscess was drained after the patient was admitted to the hospital; the patient was then discharged without further complication. The need for high-cost therapeutic methods or even death may result in instances where piriformis syndrome is overlooked by emergency department clinicians, or when it is given the misleading diagnosis of sciatalgia.