We describe considerations for carrying out ultrasound examinations in cases of common urologic emergency diseases. Urologic diseases requiring emergency surgery or treatment are limited and infrequent and comprise such conditions as trauma of the urogenital organ, rupture of a renal neoplastic mass, rupture of a renal aneurysm, renal infarction, and testicular torsion. On the other hand, those requiring palliative surgery or treatment include stones in the upper urinary tract, acute pyelonephritis, acute renal failure, acute orchitis and epididymitis, bladder tamponade, renal arteriovenous fistula, and urinary retention. When US examination is performed by a US technician or physician, the specific characteristics of pathogenesis and the ultrasonographic features of these emergency diseases should be understood. Moreover, differential diagnosis to distinguish gastrointestinal, hepatobiliary, and gynecologic emergency diseases from urologic diseases is also important.