PURPOSE/BACKGROUND: A restriction in ankle dorsiflexion range of motion (ROM) has been linked to several clinical manifestations such as metatarsalgia, heel pain, nerve entrapment, ankle joint equinus, patellar and ankle injuries. The purpose of the present study was to examine the validity and reliability of the Leg Motion system for measuring ankle dorsiflexion ROM. STUDY DESIGN: Descriptive repeated-measures study. METHODS: Twenty-six healthy male university students were recruited to test the reliability of the Leg Motion system, which is a portable tool used for assessment of ankle dorsiflexion during the weight-bearing lunge test. The participants were tested two times separated by two weeks and measurements were performed at the same time of the day by the same single rater. To test the validity of the Leg Motion system, other maximal ankle dorsiflexion ROM assessments (goniometer, inclinometer and measuring tape) were measured in a single session (i.e., the first test session) during the weight-bearing lunge position using a standard goniometer, a digital inclinometer and a measuring tape measure with the ability to measure to the nearest 0.1 cm. RESULTS: Paired t-tests showed the absence of significant differences between right and left limb measurements of dorsiflexion in all tests. Mean values ± standard deviations were as follows: Leg Motion test (left 11.6cm±3.9; right 11.9cm ±4.0), tape measure (left 11.6cm±4.0; right 11.8cm±4.2), goniometer (left 40.6º±5.2; right 40.6º±5.2), and digital inclinometer (left 40.0º±5.8; right 39.9º±5.6). The Leg Motion composite values (i.e., average of the two legs) showed a significant (p<0.05) positive correlation with the tape measure (r=0.99), with the goniometer (r=0.66), and with the digital inclinometer (r=0.72). CONCLUSIONS: The results of the present study provide evidence to support the use of the Leg Motion system as a valid, portable, and easy to use alternative to the weight-bearing lunge test to assess ankle dorsiflexion ROM in healthy participants.