Penile Mondor's disease is a thrombophlebitis of the superficial dorsal vein of the penis. It is a rare clinical diagnosis and generally resolves spontaneously. A simple physical examination is sufficient for diagnosis but color Doppler ultrasonography is often carried out as a further investigation. We describe two patients who developed priapism due to penile Doppler ultrasonography which was used for diagnosis of these patients. Now, in our opinion this examination was unnecessary.