Twenty-five cases of tubal or tubo-endometrioid metaplasia that occurred in patients from 21 to 51 years of age (mean 39 years) are described. The majority of the cases were seen in consultation. They were referred because of diagnostic problems resulting from features that have received little emphasis. The metaplasia was typically an incidental microscopic finding, although in one case metaplastic cystic glands resulted in a gross abnormality. The involved glands were usually confined to the superficial third of the cervical wall. However, in seven cases they extended more deeply. In three cases, the outer third of the wall was involved. The involved glands showed only slight variation in size and shape in 12 of the cases, but in the remainder some branching was present. Prominent cystic dilatation of the glands was seen in nine cases. The glands were typically evenly spaced, but in four cases they were focally crowded. In 22 cases, the stroma surrounding the metaplastic glands was abnormal. In 16 cases, it consisted of hypercellular endocervical stroma, and in five of these cases, the cellularity was pronounced. Four of these cases and six others focally had a loose edematous or myxoid stroma, which was pronounced in three cases. In addition to the diagnostic problems inherently associated with tubal and tubo-endometrioid metaplasia, the findings in this study, including deep glands, irregularity of gland size and shape (including cystic glands), and periglandular stromal alterations, often raised the suspicion of a premalignant or malignant glandular abnormality. Awareness that these features may be seen, as well as the often prominent ciliation of the cells, their bland cytologic features, their mitotic inactivity, and lack of an unequivocal desmoplastic stromal reaction, facilitate the differential diagnosis.