Objective: Mutations in the ABCB1 gene have an impact on the response to various drugs and may be associated with the development of neoplasms. This study explores and compares the frequency distribution of the 1236T>C polymorphism in theABCB1 gene among nine Peruvian populations from different geographical origins and altitudes, as well as the genotype/allele frequencies reported in populations from various continents worldwide. Materials and methods: Sampling was carried out in the following departments and localities: Lima (n = 8), Loreto–Andoas (n = 16), San Martín–Lamas (n = 16), Puno–Uros (n = 7), Puno–Taquile (n = 5), Arequipa–Chivay (n = 10), Arequipa–Cabanaconde (n = 6), Ancash–Parobamba (n = 10), and Apurímac–Andahuaylas (n = 10). Biological samples (peripheral blood and/or epithelial cells) were collected via buccal swabs. Deoxyribonucleic acid (DNA) was e...