Pure sex cord tumors (SCTs) are rare neoplasms derived from or display differentiation towards primitive sex cords. The tumors in this category exhibit a diversity of patterns with mimickers and accordingly may pose a diagnostic challenge. Some of the derivative cells are involved in hormone production under physiologic conditions; therefore, many tumors under this category produce excess hormones, which may lead to the development of hormone-mediated syndromes. There are clear age-related differences in the incidence of these tumors, with juvenile granulosa cell tumors, for example, occurring primarily in the <20-year age group, and adult granulosa cell tumors most commonly occurring between ages 25 and 50. The correct diagnosis of an ovarian tumor is important in all patients, but is arguably particularly so for this category, since young patients represent a proportion of patients, and issues of fertility preservation abound. This makes awareness of the diagnostic criteria and the differential diagnosis of the pure SCTs an important task. The 2020 World Health Organization classification of pure SCTs categorized four tumor types in this group. This chapter highlights all pure SCTs, with an emphasis on the clinicopathologic characteristics and advances in molecular features of each tumor, as well as a detailed discussion of differential diagnostic considerations, and the utility and limitations of immunohistochemical markers and ancillary studies in their diagnostic work-up.