Solid cell nests (SCNs) of the thyroid are single or multiple foci of solid and/or cystic clusters of squamoid cells (main cells) with a minor proportion of C-cells, found in the normal thyroid. The SCNs have also been reported in the heart as an ultimobranchial heterotopia. Here, the authors describe a case of thyroid-type SCNs associated with struma ovarii. Main cells were positive for simple and stratified epithelial-type cytokeratins, carcinoembryonic antigen, carbohydrate antigen 19.9, p63, bcl-2, and galectin-3. The neuroendocrine cell population was positive for chromogranin A and synaptophysin but negative for calcitonin, suggesting a common ancestor cell capable of dual differentiation toward thyroid follicular cells and hindgut-type endocrine cells. The existence of thyroid-type SCNs in struma ovarii could be easily understood by considering the struma ovarii as a teratoma; at the same time, these findings also support the idea of a close histogenetic link between the main cells of SCNs and thyroid tissue.