A gonadal stromal neoplasm composed only of THECA CELLS, occurring mostly in the postmenopausal OVARY. It is filled with lipid-containing spindle cells and produces ESTROGENS that can lead to ENDOMETRIAL HYPERPLASIA; UTERINE HEMORRHAGE; or other malignancies in postmenopausal women and sexual precocity in girls. When tumors containing theca cells also contain FIBROBLASTS, they are identified as thecoma-fibroma tumors with less active hormone production.