The hexagon agility test is widely used in tennis players’ fitness evaluation, although its validity has not been fully stablished. This study aimed to assess the relationships between sprinting, jumping, and change of direction (COD) ability and hexagon test performance. Thirty-five under-16 tennis players completed a testing battery including the hexagon test, 20-m linear sprint, bilateral and unilateral countermovement jumps (CMJ), triple leg-hop for distance, T-Test, 5-0-5 and Pro-Agility test on two different sessions, separated by one week. The intraclass correlation coefficient (ICC) and the standard error of measurement (SEM) were used to assess the reliability of the test. Pearson’s product correlations (r) were used to analyze the relationships between the hexagon test and the other fitness tests. Statistical significance was set at p < 0.05. The hexagon test showed high relative reliability (ICC = 0.88) and low SEM values (0.17 s). Significant small to large correlations were found between the hexagon test time and linear sprint time (r = 0.40 to 0.60), COD tests (r = 0.53 to 0.79), and jumping performance (r = -0.40 to -0.68). The hexagon test is a simple, quick, easy-to-implement and reliable test, which allow it to be included in tennis players’ testing batteries. The test is related to measures of speed, power and agility, although the magnitude of these relationships does not allow for the replacement of the more traditional assessments (e.g., CMJ, 20-m sprint, T-Test) within tennis players’ testing batteries.