Introduction: The diagnosis of Salter-Harris Type 1 fractures in the Emergency Department (ED) is primarily clinical, as radiographs are usually unrevealing. We hypothesize that bilateral asymmetry of the growth plate, detected using bedside ultrasound (US), could improve the accuracy of this diagnosis in the ED. This study seeks to determine growth plate size according to age, and to establish normal variation in bilateral symmetry of growth plate cartilage, for the ulna, radius, tibia, and fibula, using bedside US in normal healthy children. Methods: This prospective observational study was conducted in a convenience sample of children ages 0-17 during planned visits to an elementary school, high school, and an outpatient pediatric clinic. A sample size of 177 was determined with a linear regression model using previously published data on the subject. The study was approved by the hospital and universitys ethics board. After a medical questionnaire with a research nurse, the participants underwent ultrasound evaluation of bilateral ulnae, radii, fibulae, and tibiae, to obtain still images of the physes from two orthogonal views. The evaluations were performed by 3 medical residents, 1 medical student, and by the supervising emergency physician. All ultrasonographers were EDE1 certified and specifically trained for growth plate imagery. The still images were evaluated ulteriorly and measurements taken of the physeal cartilage. Ten percent of the patients had their images re-evaluated by the supervising physician to determine inter-rater reliability. Results: A total of 227 patients were recruited. The median age was 8 years old with an interquartile range of (3;14). Mean growth plate size by age was determined, confirming decreasing growth plate size with advancing age for all articulations. The percentage of absolute difference between right and left, for all growth plates together, was a mean of 17% with a 95% CI of 16-19%. The overall inter-rater reliability was excellent at 0.84. Conclusion: This study establishes a reproducible technique of measuring growth plates with ultrasound. We suspect that increased asymmetry at the growth plate, beyond this established normal variation, may signify a physis widening or hematoma consistent with a Salter-Harris Type 1 fracture; this will be evaluated in a second study.