© 2017 American Medical Association. All rights reserved. IMPORTANCE: New targeted therapies for cancer have been released in recent years, opening new horizons in the treatment of patients with cancer. However, their related adverse events (AE) are not fully characterized. Hair repigmentation (HR) is a nondescribed effect secondary to anti–programmed cell death 1 (anti–PD-1) and anti–programmed cell death ligand 1 (anti–PD-L1) therapy for treatment of lung cancer (LC), in opposition to the vitiligo reactions that develop during melanoma treatment. OBJECTIVE: To describe a new adverse event occurring during anti–PD-1/anti–PD-L1 therapy for LC. DESIGN, SETTING, AND PARTICIPANTS: A case series from a descriptive observation of 14 patients with HR after anti–PD-1/anti–PD-L1 treatment, recruited between September and December, 2016, who were followed up to detect whether they developed cutaneous AE at the time HR was detected. The patients had all been treated in the dermatology department at Hospital Universitari Germans Trias i Pujol, Badalona, Spain. MAIN OUTCOMES AND MEASURES: Clinical observation of HR during anti–PD-1/anti–PD-L1 therapy for LC, proved by comparing old pictures provided by the patients and recent pictures taken during the follow-up. RESULTS Fourteen patients (13 men and 1 woman; mean age, 64.9 years) receiving anti–PD-1 or anti–PD-L1 therapy for non–small-cell lung cancer (NSCLC) presented hair repigmentation during follow-up. This hair repigmentation consisted in a diffuse darkening of the hair in 13 of 14 patients, or in black patches between white hairs in 1. Thirteen of 14 patients presented a good clinical response to the treatment, with at least stable disease, and only 1 had to stop the therapy after only 4 cycles of treatment owing to a life-threatening progression of the disease. CONCLUSIONS AND RELEVANCE: We present to our knowledge the first report of hair repigmentation owing to anti–PD-1/anti–PD-L1 therapy for lung cancer in a series of 14 patients. Hair repigmentation may be a good response marker in patients receiving anti-PD1/anti–PD-L1 therapy for LC.