Abstract. Two cystadenomas and one solid adenoma of the thyroid gland in a 27-year-old female African green monkey (Chlorocebus aethiops) are described here. Histologically, the solid
adenoma was classified as a well-defined solid follicular adenoma of
microfollicular type. The solid adenoma was positive for thyroglobulin in
immunohistochemistry staining, whereas the cystadenomas stained positive for both thyroglobulin and calcitonin. No evidence of excess hormone production related to the tumor presence was detected.