Chromomycosis is a chronic fungal disease of the skin and subcutaneous tissues caused by a group of dematiaceous black fungi. Small lesions can be removed with excision, but other cases are difficult to treat. We report a case of chromomycosis caused by Fonsecaea pedrosoi (F. pedrosoi). The case involved a 74-year-old man, who had noted a lesion on the back of the right thigh, that was gradually enlarging and reaching up to 30 cm in diameter, in 20-years. From microscopic examination, sclerotic cells were seen. We diagnosed this case as chromomycosis caused by F. pedrosoi on mycological examination. The patient was initially treated with oral terbinafine (250 mg/day) as the lesion was very large. After the 18 months treatment, the size of the lesion reduced to 1 cm, then the remaining lesion was excised.