Ovarian torsion occurs when the ovary (and often the fallopian tube) twists on its ligamentous pedicle, compromising blood supply. It is a gynecologic emergency requiring prompt surgical intervention. Ultrasound findings include an enlarged ovary (often >4 cm), peripheral follicles displaced to the cortex by stromal edema, and a twisted pedicle that may show a whirlpool sign on color Doppler. Importantly, the presence of Doppler flow does not exclude torsion — partial torsion can preserve some vascularity. Clinical correlation is essential.