Failure and degradation mechanisms of plastic packaged LEDs that have been subjected to high levels of moisture, current bias, and elevated temperature conditions have been investigated and analyzed. The investigation included electrical characterization and a variety of failure analysis techniques including photoluminescence (PL), electroluminescence (EL), cathodoluminescence (CL), and environmental scanning electron microscopy (ESEM). Our results highlight the usefulness of simple screening techniques to monitor the quality of newly manufactured LED packages. Our results also indicate that for AlGaAs structures, degradation of the light output and electrical performance involves a complex interaction between temperature, relative humidity at the LED surface and voltage bias.