Proper in vitro mechanical testing of medical devices requires consideration of many factors, including environmental conditions, implant characteristics, and nature of the test method. In this study, parallel plate compression testing of porous specimens composed of 75:25 poly(D,L-lactide-co-glycolide) reinforced with short polyglycolide fibers was used to show the effect of many factors on the compressive modulus and yield strength. Compressive properties were dramatically reduced when tested under physiological conditions (aqueous, 37 °C) versus ambient conditions. Predominant fiber alignment yielded superior properties when tested parallel to the fiber orientation, increasing the compressive properties proportionally with fiber content from 0% to 20%. With increasing strain rate over four orders of magnitude, compressive moduli increased logarithmically and yield strength increased in a semi-logarithmic fashion. After in vitro degradation for nine weeks, compressive properties decreased to less than 20% of their original values.