Variations between measurements of clinical outcomes sometimes result from observer errors and are not due to the therapeutic intervention. For the correct interpretation of clinical data it is, therefore, important to ascertain the reliability of the measurement methods used. In the present study we evaluated the test-retest and between observer reliability of gait measurements with the Cartesian Optoelectronic Dynamic Anthropometer (CODA mpx30) motion analysis system. Our findings suggest a better intra-rater and inter-rater reliability of kinetic than kinematic data. Disagreements between the investigators were most marked for the kinematic data, especially the hip angle, and disagreements were least for the spatio-temporal gait parameters. The poor reproducibility of kinematic variables may be due to problems with the accurate placement of markers on the surface anatomical landmarks.