In the present investigation, the mechanical properties of natural polyether-ether-ketone (PEEK), processed by additive manufacturing applying fused deposition modeling (FDM) with three different infill densities, are investigated. Mechanical characterization was performed through destructive testing. Specimens were designed in CAD software and printed with controlled infill densities of 40%, 70%, and 100%, using a rectilinear pattern. The results showed that increased infill density improves mechanical strength and stiffness but reduces ductility and energy absorption capacity. For considered infill densities, maximum stress levels reach values of 107.53±6.29MPa, 114.32±11.95MPa, and 63.96±2.39MPa, respectively, against compression, bending, and tensile loading. These findings offer crucial information for optimizing infill density in manufacturing high-strength components for industrial and biomedical applications. As a result, practical guidelines are provided for the design of medical devices, such as implants, achieving an appropriate balance between mechanical performance and material efficiency.