Objective: To analyze the reliability of a questionnaire to assess physical activity in a sample of school adolescents living at high altitude through internal consistency and test re-test. Materials and methods: Descriptive, transversal (Survey). Universidad Nacional del Altiplano (Puno, Peru). School Teens 12 to 17 years. There were systematically selected 109 students of both sexes. We evaluated anthropometric measurements of weight, height, sitting height and circumference of the abdomen. In addition we applied a physical activity questionnaire with 11 questions (test and re-test) with an interval of 7 days. capacity rating for internal consistency, reproducibility and stability. Results: Cronbach’s alpha values (internal consistency) showed values from 0.73 to 0.77 for both sexes. Measuring technical error (SEM) was from 0.50 to 1.61% and the Spearman correlation coefficient ranges from 0.91 to 0.95. Conclusion: The physical activity questionnaire shows high values of reliability, consistency both internally and in the stability of the measures.