Mucinous epithelium is the most uncommon type identified in ovarian adenofibromas. Because of the rarity of mucinous adenofibromas and the presence of cytologic atypia in some, these neoplasms may be mistaken for low-grade metastatic adenocarcinoma. The clinicopathologic features of 10 mucinous adenofibromas are reviewed. They occurred in women 24 to 76 (mean, 51) years of age, were unilateral, and ranged in diameter from 1 to 25 cm. Seven tumors were classified as benign, containing glands lined by a single layer of mucin-containing columnar cells. Three tumors that contained crowded glands lined by mucin-containing cells with mild to moderate nuclear atypia, nuclear stratification of up to three cells in thickness, and focal tufting were classified as benign with epithelial atypia. Most women had a hysterectomy and bilateral salpingo-oophorectomy. Follow-up information was available on six women, who were alive and well from 6 to 126 (mean 41) months after diagnosis. The identification of mucinous glands in typical fibromatous stroma should allow the distinction of these benign neoplasms from metastatic carcinomas.