Background: The maximum rate of oxygen consumption (V̇O2max) can be measured through numerous tests, either directly or indirectly, where direct methods are considered more accurate, whereas indirect methods are more of an estimation with various degrees of reliability. Cooper's Test is one example of an indirect method considered reliable in estimating V̇O2max, with reliability coefficients ranging between 0.897-0.960. Cooper's Test is thus a test that is often used when estimating V̇O2max. However, there is a lack of test-retest research done utilising Cooper's Test on a younger population, which is the reasoning behind this study focusing on adolescents. Aim: The aim of the study was to study the test-retest reliability of Cooper's Test, in adolescents aged 16-19 years. Methods: Twelve healthy adolescents, aged 16-19 years, attending a sports high school participated in a test-retest study (test 1 and test 2) of Cooper's Test. The tests were performed on the short sides of a synthetic grass field, with 66 metres between the two sides, were the participants were instructed to cover as much distance as possible, with high motivation and intensity, for the whole 12 minutes of the Cooper's Test. Each individual participant's data was measured, recorded and later analysed. The total distance covered was then translated into miles and compared to Cooper's original estimated maximal oxygen consumption table for an estimation of each participant's V̇O2max value in ml*kg-1*min-1 from test 1 and test 2. The data from the test-retest and its variance was then analysed by a two-way mixed model of intraclass correlation coefficient (ICC) with an absolute agreement type. Results: The analysed data from test 1 and test 2 of Cooper's Test showed the results of an ICC (95% CI) of 0.06 (-0.353 to 0.544), indicating a substantial error variance between the two separate Cooper's Tests. Conclusion: The data and analysis from this study implied that Cooper's Test was not reliable in the study population, consisting of adolescents. Possible factors influencing the result however were lack of participant motivation and the level of intensity variance during the test-retest of Cooper's Test. Further researchers and amateur and professional users should keep these factors in mind when utilising Cooper's Test to predict V̇O2max. More research is needed within this study's age population to draw any definite conclusions on the reliability of Cooper's test on adolescents.