Objective: Hirsutism and hyperandrogenism in premenopausal women are most often associated with polycystic ovarian syndrome (PCOS). We present a case of progressive, severe hyperandrogenism with negative imaging identified on surgical histopathology as being due to a Leydig cell tumor, thus illustrating localization challenges associated with these small tumors. Methods: Laboratory investigations included testosterone, dehydroepiandrosterone sulfate (DHEAS), 17α-hydroxyprogesterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid stimulating hormone (TSH), 24-hour urine cortisol (UFC), and prolactin. Imaging included pelvic ultrasound, adrenal magnetic resonance imaging (MRI), and computed tomography (CT). Ovarian vein sampling was not available. Results: A 42-year-old woman presented with frontal alopecia, voice deepening, coarse facial hair, and amenorrhea on a background of lifelong oligomenorrhea. Peak testosterone was 30.2 nmol/L (female range < 2.0) with normal DHEAS, 17-OH progesterone, prolactin, UFC and TSH. Transvaginal ultrasound, adrenal MRI and CT thorax/abdomen revealed no androgen source. Testosterone failed to suppress with GnRH agonist. Although no abnormality was seen during oophorectomy, surgical pathology documented a 1.8 cm well-circumscribed hilar Leydig cell tumor. Post-operative testosterone was < 0.5 nmol/L. Conclusion: Although this patient had testosterone levels well into the masculine range, multiple imaging results were negative with a Leydig cell tumor found only after oophorectomy. Leydig cell tumors are rare ovarian stromal tumors and while 50–70% of these tumors produce androgen, size and clinical severity may not be well correlated. This case report illustrates that despite an association with substantially elevated androgen levels, the small size of Leydig cell tumors can result in localization challenges.