The optical damage resistance of diffused lithium niobate wave-guides is discussed. Long-term laser power handling performance is assessed by recording the spatial intensity changes occurring as a function of time in a waveguide's far field. Out-diffused waveguides are found to offer significantly greater long-term resistance to optical power losses caused by optical damage than do waveguides formed by either ion exchange or titanium in-diffusion. Any waveguide's resistance to optical damage is lowered by inadvertent exposure to chemical reducing conditions that can prevail during device fabrication processes. Waveguides exposed to the severe chemical reducing conditions are found to exhibit dramatically nonlinear behavior when exposed to high laser powers and short laser wavelengths.