INTRODUCTION 3D printing for non‐weight‐bearing upper extremity prostheses is becoming increasingly popular as a method of fabrication.1 Some clinics in North America have begun using 3D printing to fabricate lower extremity diagnostic sockets (Figure 1). The strength requirements for upper extremity prostheses are not as rigorous as the strength requirements for lower extremity prostheses. Therefore, strength testing on 3D-printed lower extremity sockets is one of the first steps that needs to be conducted to ensure patient safety. 3D-printed prosthetic sockets are becoming an alternative option to traditional methods because it is possible to customize different parameters to create a strong structure. Infill percentage is an important parameter to research as this can have an influence on the strength of 3D printed sockets.2 As both prosthetists and healthcare professionals, there is a need to become more involved in the process of designing and testing 3D printed sockets. The purpose of this study is to test how changing the infill percentage affects the ultimate strength of a 3D printed transtibial socket during initial contact. Abstract PDF Link: https://jps.library.utoronto.ca/index.php/cpoj/article/view/32038/24453 How to cite: Campbell L, Lau A, Pousett B, Janzen E, Raschke S.U. HOW INFILL PERCENTAGE AFFECTS THE ULTIMATE STRENGTH OF A 3D-PRINTED TRANSTIBIAL SOCKET. CANADIAN PROSTHETICS & ORTHOTICS JOURNAL, VOLUME 1, ISSUE 2, 2018; ABSTRACT, POSTER PRESENTATION AT THE AOPA’S 101ST NATIONAL ASSEMBLY, SEPT. 26-29, VANCOUVER, CANADA, 2018. DOI: https://doi.org/10.33137/cpoj.v1i2.32038 Abstracts were Peer-reviewed by the American Orthotic Prosthetic Association (AOPA) 101st National Assembly Scientific Committee. http://www.aopanet.org/