The purpose of this study was to evaluate the reliability of a new developed device to measure tibial rotation, the Rotameter. Thirty healthy subjects (15 males, 15 females, 24 years) were examined with the Rotameter measurement device. External and internal rotation was performed at an applied torque of 5, 10 and 15 Nm by two independent examiners in order to test the inter-observer reliability. The patients were measured again after a mean of 31 +/- 43 days by the same examiners to test the intra-observer reliability. Statistical analysis was performed using the intra-class correlation coefficient. The Pearson Correlation coefficient was used to compare the measurements of the left with the right side of the participants. In the measurements, a high inter- and intra-observer reliability was found at 5, 10 and 15 Nm of applied torque for the external rotation, internal rotation and the rotational range (internal + external rotation). Comparison of the left and the right knee of the same participant also revealed high correlations in the Pearson correlation coefficient at all applied torques. In conclusion, the Rotameter testing device for the measurement of tibial rotation showed a high inter-observer and intra-observer reliability. It is easy to perform and might be used in a wide field as a non-invasive instrument to objectively determine rotational stability and to investigate the restoration of the rotational stability after surgical procedures.