Perivascular epithelioid cell tumors (PEComas) are a very rare group of neoplasms and were first reported in 1996. These tumors represent a family of mesenchymal neoplasms, related through activation of the mammalian target of rapamycin (mTOR) inhibitor signaling pathway. The objective of this case report is to demonstrate significant regression of the tumor after neoadjuvant treatment with an oral mTOR inhibitor, following surgical removal of the mass to avoid a multiorgan resection. We present a case of a 27-year-old female with retroperitoneal PEComa and evaluated the tumor with MRI and integrated 18F-FDG-PET/CT scans at presentation and serially during treatment with everolimus. After 6 months of treatment with everolimus the tumor showed a substantial size reduction. Therefore, a multiorgan resection could be omitted. The patient has not demonstrated any disease recurrence after nearly 2 years of follow-up. PEComas are tumors with unpredictable behavior. Our report indicates that treatment of PEComas with everolimus may achieve a significant clinical response. As indicated by our case and past reports, mTOR inhibitors may be one of the best treatment options for this disease.