Vaginal adenosis was evaluated in 41 women, all of whom had been born prior to the diethylstilbestrol (DES) era, and compared with the adenosis commonly encountered in DES-exposed progeny. The patients were 24 to 88 years of age (median, 44 years). Six of the women were symptomatic, and in four of these six the glands were enmeshed in a marked inflammatory infiltrate. In an additional 26 women the adenosis was discovered as incidental, nonsymptomatic macroscopic nodules or cysts. The remaining nine cases of adenosis were discovered by pathologists. Three types of epithelia characterized the glands: mucinous, tuboendometrial, and embryonic. Mucinous columnar cells resembling the lining of the normal endocervix and tuboendometrial cells resembling the lining of the normal fallopian tube or endometrium constituted the glands exclusively in 22 and eight specimens, respectively, and as a mixture in seven. The glands lined by mucinous cells most often presented clinically as cysts or nodules. The specimens composed of tuboendometrial cells were most often discovered on microscopic examination. The third type of epithelium, composed of embryonic columnar cells, was encountered in four specimens. These glands, less than 30 micron in greatest diameter, were located at the junction between the lamina propria and the squamous epithelium, and were incidental microscopic findings. It is concluded that the microscopic appearances of adenosis in women born prior to the DES era are identical to those encountered in young women exposed in utero to DES.