Fungal infection of the thyroid is rare. Most reported cases have involved Aspergillus, Coccidioides, and Candida species in the setting of disseminated disease. Infection of the thyroid with Histoplasma capsulatum is rarely reported as part of disseminated disease, even in geographic areas where histoplasmosis is endemic. We report a 52-year-old woman with a previous Hashimoto's disease and non-Hodgkin's lymphoma in which a diffuse enlarged thyroid gland with a large nodule was the only apparent locus of histoplasmosis. Fine-needle aspiration of the thyroid was an important diagnostic tool in establishing the diagnosis of histoplasmosis of the thyroid. The patient was initially treated with itraconazole (400 mg/day) for the fungal infection and six cycles of chemotherapy for the lymphoma. At a 6-month follow-up examination, the patient was doing well on suppressive therapy of itraconazole (200 mg/day), with no symptoms and with regression of the thyroid nodule and cervical adenopathy.