Background <p>Metal lattice structures are increasingly used in engineering applications due to their multifunctional capabilities. However, detecting early-stage fatigue damage in these structures remains a challenge.</p> Objective <p>This study aims to evaluate the effectiveness of acoustic resonance testing in detecting fatigue damage in metal lattice structures by correlating shifts in resonance frequencies with crack initiation and propagation.</p> Methods <p>Metal lattice specimens composed of primitive Schwartz unit cells were subjected to fatigue loading at a stress ratio of 0.1 and constant amplitude. Fatigue tests were interrupted at 10%, 5%, and 2.5% reductions in global stiffness to assess progressive damage. Acoustic resonance testing was conducted on each specimen before and after fatigue testing under two boundary conditions: simply supported and clamped-clamped, the latter achieved by installing the specimen directly in the fatigue testing machine. Additionally, two specimens were monitored using acoustic resonance testing during the fatigue test to observe <i>in-situ</i> spectral changes.</p> Results <p>Across all configurations, resonance frequency shifts were observed and correlated with stiffness degradation and visual evidence of crack growth. The acoustic response consistently reflected damage evolution, demonstrating sensitivity to both crack initiation and propagation stages.</p> Conclusions <p>Acoustic resonance testing is shown to be a reliable and sensitive method for detecting fatigue damage in metal lattice structures. The strong correlation between resonance shifts and fatigue damage progression highlights its potential for real-time structural health monitoring and improved maintenance strategies.</p>