Malignant melanoma can be successfully treated when it is identified in its early stages, but the disease is associated with a poor prognosis when it is detected in an advanced stage. Papillary thyroid carcinoma is a thyroid cancer that has a good prognosis. The present study reports a rare case of malignant melanoma and papillary thyroid carcinoma that were diagnosed concurrently and treated simultaneously. The present patient was a 37-year-old male, in whom examination of a skin biopsy that was obtained from a lesion in the right retroauricular region revealed the lesion to be consistent with malignant melanoma. The patient underwent radical neck dissection upon the detection of malignant melanoma metastasis to the sentinel lymph node. Metastases of papillary thyroid carcinoma were detected in four out of 38 lymph nodes. The patient was then diagnosed with papillary thyroid carcinoma and underwent total thyroidectomy. The patient was administered with high-dose followed by moderate-dose interferon-α therapy for the treatment of malignant melanoma. The patient also received concurrent radioactive iodine therapy for the treatment of papillary thyroid carcinoma, at the same time as the interferon therapy. The two primary tumors of the patient were treated successfully. During therapy, no serious side-effects were observed, with the exception of fever caused by high-dose interferon therapy. Malignant melanoma and papillary thyroid carcinoma may occur concurrently, although this is rarely observed. The present study reports a rare case that demonstrates that the two tumors can be successfully treated simultaneously.