Compared to measuring static range of motion (ROM) the assessment of dynamic ROM has received very little research attention. The purpose of this study therefore was to determine the reliability of the siliconCOACH motion analysis system for assessing dynamic ROM of the knee joint.Test-retest reliability.Laboratory.Ten male subjects unable to fully extend their knee at 90° of hip flexion.Static and dynamic ROM over four separate occasions using a video camera and siliconCOACH digitized footage.The variation between days for both static and dynamic measurements was minimal (CV<2.1%). With regards to test-retest reliability, the ICC values, were high (ICC⩾0.89) for both assessment techniques and the static and dynamic ROM measurements did not differ significantly (p<0.05) on any given testing occasion.The high ICC and low CVs indicate a high degree of stability between testing days for the procedures used in this study to assess dynamic ROM. Software programmes such as siliconCOACH seem ideal for determining the end range of a movement for both static and dynamic ROM and would seem to offer a functional and cost effective assessment strategy for those practitioners and clinicians interested in the effects of various interventions on ROM.