The hair and nails are complex cutaneous adnexal structures influenced by the patient's physiologic state. Systemic diseases may affect either or both. Remote internal malignancies may induce skin changes that are neither genetically related nor part of a tumor syndrome. The treatment of cancer with chemotherapy and radiation therapy may also induce abnormalities of the hair and nails. In this article, various paraneoplastic and cancer treatment-related hair and nail changes are described. The proper evaluation of such abnormalities may allow for the prompt and efficient diagnosis and management of an internal malignancy. Establishing an understanding of hair and nail abnormalities can be vital in assessing a patient's overall health, especially in the context of cancer detection and treatment.