Abstract Introduction/Objective The co-existence of basal cell carcinoma (BCC) and systemic mastocytosis is an exceptionally rare clinical occurrence, and the prognosis is not well-documented. Understanding the clinical and histopathological features of this uncommon association is relevant for accurate diagnosis, management, and prognostication. Methods/Case Report We conducted a retrospective analysis of three cases of BCC with concurrent systemic mastocytosis that were identified in the pathology database of the University of Pennsylvania from 2010 to 2023. Patient demographics, clinical and histopathologic characteristics, and treatment outcomes were reviewed. Histopathologic assessment, immunohistochemistry, and C-KIT D816V mutation analysis (with an allele-specific PCR assay) were performed on biopsy material. Next-Generation Sequencing (NGS) was used to identify other hematologic neoplasm-associated mutations. Results (if a Case Study enter NA) All three cases were female with a median age of 55.3 years (50, 69, 47). In all three cases, atypical CD117+ tryptase+ CD25+ mast cells with mild to moderate pleomorphism were found in the dermis adjacent to the BCC cells. All three cases had bone marrow involvement. Serum tryptase levels were mildly elevated in all 3 patients (maximum 65.5 μg/L). All three cases harbor a C-KIT D816V mutation and a history of systemic glucocorticosteroids before the diagnosis of BCC. One of the cases was treated with phototherapy. NGS detected the following somatic mutations: Case #2 DNMT3A p.R882H c.2645G>A; Case #3 JAK2 V617F. Case #1 had multiple relapses of BCC, but a subsequent marrow biopsy did not identify any involvement by mastocytosis. Case #2 had mast cell leukemia, which typically has a poor prognosis; however, this patient has survived for several years. Case #3 had essential thrombocythemia and systemic mastocytosis with an associated hematological neoplasm, and her symptoms were stable. Treatment modalities for the three patients ranged from surgical excision to anti-mastocytosis therapy, with favorable outcomes (Table 1). Conclusion The coexistence of BCC with mastocytosis poses diagnostic challenges due to its infrequency and varied clinical presentations. Previous literature reports on treatments of mastocytosis such as phototherapy and steroids, which have been identified as risk factors for the development of basal cell carcinoma. However, recognizing this unique combination in clinical practice may aid in providing appropriate treatment strategies, ultimately leading to favorable patient outcomes.