Herein, we report a rare case of amelanotic spindle-cell melanoma on the interdigit of the left fifth toe of an 83-year-old woman. She also had tinea pedis on the same part for more than 2 years, and the part in which the tumor developed had been macerated and colonized with both Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus. Histopathologically, the biopsy specimen was indistinguishable from that of nonspecific inflammatory granulation. Two biopsies could not lead us to the correct diagnosis until the totally excised specimen was evaluated with immunohistochemical analysis including S-100 and other melanocyte markers. The patient died with multiple metastases of the tumor 18 months after her first visit. This case suggests that refractory interdigital dermatophytoses should be treated by considering the possibility of concomitant malignant neoplasms, and immunohistochemical analysis is indispensable for differential diagnosis of malignant neoplasms suggesting nonspecific granulation.