The sonograms of 76 hemorrhagic ovarian cysts were reviewed to ascertain the full spectrum of sonographic findings. All cases were proved either by surgery or by documented resolution on sonography and/or clinical follow-up. The overwhelming majority (92%) had increased sound through-transmission, signifying the basic cystic nature of the lesion. The sonographic patterns were variable. The most common appearance was that of a heterogeneous mass (83%), almost half of which were predominantly anechoic with hypoechoic material. The other cases (17%) were completely homogeneous, either hypo- or hyperechoic. No masses were completely anechoic. Additional sonographic features included a thick rim, septations, and associated cul-de-sac fluid. A rounded hyperechoic mass, representing blood clot, was contained within 13 masses. In addition, some women appeared to have an increased tendency to form ovarian cysts, suggested by the fact that 26% of them had a past, concurrent, or future episode of simple or hemorrhagic ovarian cysts. Because hemorrhagic ovarian cysts have variable sonographic findings, they should be included in the differential diagnosis of any adnexal mass that has good sound through-transmission.