Castagna, C, Ganzetti, M, Ditroilo, M, Giovannelli, M, Rocchetti, A, and Manzi, V. Concurrent validity of vertical jump performance assessment systems. J Strength Cond Res 27(3): 761–768, 2013—The aim of this study was to examine the concurrent validity of 2 portable systems for vertical jump (VJ) assessment under field conditions. The VJ flight times assessed using an optical mat (Optojump) and an accelerometer-based (Myotest) system were compared with that of a force platform. The flight times recorded during a countermovement jump (CMJ) were collected from 20 rugby players (n = 86 jumps) concurrently using the 3 tracking systems. Significant bias between the Force platform and either the Optojump (bias = 0.006 ± 0.007; 95% confidence interval [CI] 0.004–0.007 seconds) and Myotest (bias = −0.031 ± 0.021; 95% CI 0.035 to −0.026s; p < 0.0001) occurred. A nearly perfect correlation was found between force platform and Optojump (r = 0.99; 95% CI 0.098–0.99; p < 0.0001). Force platform and Myotest (r = 0.89; 95% CI 0.084–0.93; p < 0.0001) flight times showed very large association. Difference between Optojump and Myotest systems was significant (−0.036 ± 0.021 seconds; 95% CI −0.041 to −0.032; p < 0.0001), which results in Myotest mean flight time being approximately 7.2% longer than the Optojump flight time. The association between Optojump and Myotest was nearly perfect (r = 0.91, 95% CI 0.86–0.94; p < 0.0001). This study showed that the Optojump and Myotest systems possess convergent validity and can be successfully used under field conditions to assess VJ while performing a CMJ. However, caution should be exercised when interpreting data obtained from different portable systems for field measurement.