A healthy ovary produces a normal physiologic cyst with each menstrual cycle in women during the reproductive years (ages 12-52). During menarche, as well as during the perimenopausal period, this normal process occurs less frequently. The normal cyst or follicle contains the egg or ovum and usually is less than 3 cm. in size. After ovulation, this cyst persists in the form of a corpus luteum and is also normal and physiologic. These cysts are rarely greater than 5 cm., resolve with each menstrual cycle, are simple in appearance, and are not suggestive of ovarian cancer. Cysts that persist throughout multiple cycles, are 6 cm. or larger, are complex, or are formed during childhood or after menopause, are considered abnormal. However, the vast majority of these are benign. Further diagnostic evaluation of this group of cysts is warranted, as a very small fraction may be ovarian cancer.