To evaluate the validity of an integrated accelerometer and Global Positioning System (GPS) device to quantify swimming kinematics variables in swimming.Criterion validation study.Twenty-one sub-elite swimmers completed three 100 m efforts (one butterfly, breaststroke and freestyle) in an outdoor 50 m Olympic pool. A GPS device with an integrated tri-axial accelerometer was used to obtain mid-pool velocity and stroke count of each effort. This data was compared to velocity and stroke count data obtained from concurrently recorded digital video of the performance.A strong relationship was detected between the accelerometer stroke count and the video criterion measure for both breaststroke (r>0.98) and butterfly (r>0.99). Also, no significant differences were detected between the GPS velocity and video obtained velocity for both freestyle and breaststroke. There was a significant difference between the GPS velocity and criterion measure for butterfly. Acceptable standard error and 95% limits of agreement were obtained for freestyle (0.13 m s(-1), 0.36 m s(-1)) and breaststroke (0.12 m s(-1), 0.33 m s(-1)) compared to butterfly (0.18 m s(-1), 0.50 m s(-1)). Relative error measurements ranged between 10.2 and 13.4% across the three strokes.The integrated accelerometer and GPS device offers a valid and accurate tool for stroke count quantification in breaststroke and butterfly as well as measuring mid-pool swimming velocity in freestyle and breaststroke. The application of GPS technology in the outdoor training environment suggests advantageous practical benefits for swimmers, coaches and sports scientists.