The transvaginal ultrasound echo patterns of 39 surgically proven cystic teratomas were retrospectively reviewed. Six different ultrasound echo patterns could be differentiated, ranging from purely cystic to densely echogenic. Importantly, in 82% of the tumors, areas of dense echogenicity were noted. Although the transvaginal appearance of cystic teratomas may allow correct preoperative prediction, the variable nature of the echo patterns makes differentiation from malignant tumors difficult.