Birt-Hogg-Dubé syndrome (BHDS) is an autosomal dominant genodermatosis characterized by benign cutaneous tumors (fibrofolliculomas, trichodiscomas, and acrochordons), basal lung cysts, pneumothoraces, and a 20% to 30% lifetime risk for renal cancer. There are isolated cases of other cancers in BHDS reported in the literature, including oncocytoma, rhabdomyoma, melanoma, thyroid cancer, meningioma, colon cancer, and breast cancer, but only the increased renal cancer risk has been substantiated. This is the case of a 9-year-old girl who presented with a leiomyosarcoma whose tumor genetic analysis showed FLCN c.365_372del, p.Arg122Leufs*8. She was diagnosed with BHDS when the same mutation was confirmed in her germline lymphocytes. This is the second known reported case of leiomyosarcoma in BHDS.