The objective of this study was to determine the levels of malondialdehyde (MDA), an oxidative stress biomarker, in individuals living at high altitudes (3500-4200 m). This exploratory study evaluated 91 subjects from La Paz and El Alto using a questionnaire and clinical examination. MDA levels were measured using a colorimetric technique. Measures of central tendency, dispersion, and percentages were used to describe data, and the Mann-Whitney test and Kruskal-Wallis test were used to assess differences between the sexes, age groups, and altitudes. The median concentration of MDA was 4.1 μmol/L (RIC 2.4-5.4) and the highest concentration of MDA was found in individuals older than 40 years. The average MDA levels were higher than those found at sea level, a result we believe is due to the effect of hypoxia. However, there were no differences in the MDA levels between the sexes or age groups.