Tehran University of Medical Sciences Journal of Pharmaceutical Care 2322-4630 13 2 2025 06 30 144 147 Farshad Abedi Department of Clinical Pharmacy, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran Negin Allahyari Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Abolghasem Allahyari Department of Hematology and Oncology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Omid Arasteh Department of Clinical Pharmacy, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran Ahmad Reza Taheri Department of Dermatology, Cutaneous Leishmaniasis Research Center, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. 2025 01 12 2025 04 22 Letrozole, a nonsteroidal aromatase inhibitor, is the adjuvant endocrine treatment for postmenopausal women with estrogen receptor-positive breast cancer. Erythema nodosum (EN) is a rare skin adverse effect of letrozole which has been previously reported in a few case reports. We report a new case of EN-induced by letrozole in a 63-year-old Iranian woman with left breast cancer who was estrogen receptor-positive. Physical examination and laboratory findings were consistent with EN. Manifestations resolved following discontinuation of letrozole and treatment with oral prednisolone. This case highlights EN as a potential adverse effect of letrozole. Clinicians should be aware of this rare but significant reaction, as early recognition and discontinuation of the offending agent can lead to complete resolution of symptoms. https://jpc.tums.ac.ir/index.php/jpc/article/view/793 https://jpc.tums.ac.ir/index.php/jpc/article/download/793/423