The durability of a commercially available injection molding grade polylactide (PLA) was assessed by exposure to conditions of elevated temperature and humidity over a period of several weeks. Moisture absorption, molecular weight, and mechanical performance were monitored over time and as a function of crystallinity level. At 50 degrees C and 90% relative humidity, both amorphous and crystalline samples of PLA showed significant moisture absorption, allowing hydrolysis to occur. The study showed that while crystalline content had an effect on the initial moisture absorption behavior, the overall longer term effects on degradation were surprisingly minor. A cumulative damage model was used to relate the overall degradation due to moisture uptake and hydrolysis to long-term durability in environments typical of automotive interiors. The study showed that the injection molding grade PLA resins that are currently commercially available are not suitable for use in applications that require long-term durability in environments subject to elevated temperature and humidity. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1380-1389, 2010