Poor posture control has been associated with an increased risk of falls and mobility disability among older adults. This study was conducted to assess the test–retest reliability and sensitivity to group differences regarding the time-limit (T Limit ) of one-leg standing and selected balance parameters obtained with a force platform in older and young adults. A secondary purpose was to assess the relationship between T Limit and these balance parameters. Twenty-eight healthy older adults (age: 69±5years) and thirty young adults (age: 21±4years) participated in this study. Two one-leg stance tasks were performed: (1) three trials of 30s maximum and (2) one T Limit trial. The following balance parameters were computed: center of pressure area, RMS sway amplitude, and mean velocity and mean frequency in both the anterio-posterior and medio-lateral directions. All balance parameters obtained with the force platform as well as the T Limit variable were sensitive to differences in balance performance between older and young adults. The test–retest reliability of these measures was found to be acceptable (ICC: 0.40–0.85), with better ICC scores observed for mean velocity and mean frequency in the older group. Pearson correlations coefficients (r) between balance parameters and T Limit ranged from −0.16 to −0.54. These results add to the current literature that can be used in the development of measurement tools for evaluating balance in older and young adults.