In hysterosalpingo-contrast sonography (HyCoSy), contrast media is injected into the uterus through a catheter that is placed in the cervical canal. The flow of contrast through the fallopian tubes into the pouch of Douglas is examined in order to verify whether there is partial or total occlusion or any other pathology of the tubes. This is an outpatient method of investigation for female fertility. Procedure performance and interpretation are discussed in this chapter. HyCoSy with saline and air has excellent negative predictive power, which means that if tubes are patent with this contrast, there is no need for further investigation. If necessary, more powerful methods can be used, such as using contrast foam with two- or three-dimensional high-resolution Doppler flow ultrasound.