Ovarian involvement by metastatic colorectal adenocarcinoma, although not an uncommon occurrence, remains a diagnostic challenge. The gross and histologic features of such metastases overlap those of primary ovarian epithelial neoplasms such as endometrioid or mucinous adenocarcinoma. The clinical and pathologic features of 86 cases of metastatic colorectal adenocarcinoma involving the ovary were reviewed. Patients ranged in age from 19 to 85 years (median, 51 years); 24% were younger than 40 years. Presenting symptoms included abdominal or pelvic pain (45 cases), rectal bleeding (13 cases), change in bowel habits (20 cases), and vaginal bleeding (5 cases). In 23 cases, an ovarian mass was the first manifestation of the disease. Ovarian involvement was bilateral in 49 cases and unilateral in 33 (including 20 cases in which the only involved ovary measured at least 10 cm in greatest dimension). Involved ovaries ranged from 2 to 24 cm (mean, 10.1 cm), and most featured both solid and cystic areas. Many involved ovaries featured smooth capsules without gross evidence of surface involvement by tumor. In general, the tumors had typical histologic features of metastatic colorectal adenocarcinoma, including a garland pattern and dirty necrosis. In 23 cases, foci with a benign or low malignant potential appearance were seen. Immunohistochemical studies showed that 29 of 29 tumors (100%) were positive for CK20; focal CK7 positivity was seen in 5 of 30 cases (17%). In 9 of the cases, an ovarian primary was diagnosed or favored initially, and 5 of these cases were initially treated as ovarian primaries. Metastatic colorectal adenocarcinoma should be considered in the differential diagnosis of an ovarian mass, even if the mass is large and unilateral or in a young patient, to secure proper treatment of these patients.