Ovarian tumors encountered during pregnancy can pose a diagnostic challenge due to an abundance of luteinized cells and other changes. We report 8 sclerosing stromal tumors with massive luteinization discovered in pregnant patients. The tumors ranged from 3.1 to 21 cm (mean=8.8 cm) in size and were typically solid and yellow; the neoplasm was bilateral in 1 case. On microscopic examination, the lutein cells, a feature of sclerosing stromal tumor, had more copious eosinophilic cytoplasm and were more numerous than is usually seen in nonpregnant patients and to varying degrees obscured the typical pseudolobular pattern. This resulted in particular diagnostic difficulty in 3 cases, especially when associated with other changes including irregular shapes of tumor cell nests, edema, and/or myxoid change. However, classic features of these tumors: ectatic vessels and admixed luteinized and nonluteinized cells were still focally evident, allowing for accurate classification. The tumors were cytologically bland and with 1 exception had rare mitoses. As sclerosing stromal tumors have been invariably benign, it is important that they not be confused with other tumors, such as steroid cell tumor, which can occasionally be malignant.