Background: Primary mucinous adenocarcinoma of the skin is a rare malignant sweat gland tumor, which is difficult to distinguish from metastatic adenocarcinoma. Purpose: Describe a case of mucinous adenocarcinoma of the scalp and discuss the usefulness of immunohistochemical techniques in the diagnosis of primary vs. metastatic mucinous adenocarcinoma. Case Report: A 58 year old female presented with a cyst on her scalp, which was initially diagnosed as a metastatic mucinous adenocarcinoma. After radiological evaluation the malignancy was determined to be a primary mucinous adenocarcinoma of the scalp. Treatment included wide excision and radiation therapy with no recurrence or metastasis on follow up. Conclusion: This case report describes challenges in the diagnosis of primary vs. metastatic mucinous adenocarcinoma of the skin.