Gait biomechanics have been studied extensively. Many existing studies, though, have been performed in a controlled laboratory setting, and assumed that measures obtained are representative of gait in a naturalistic environment (e.g., outdoors). Several environmental and psychological factors may contribute to differences between these environments, and identifying any such differences is important for generalizing results outside the laboratory. The purpose of this study was to test the implicit assumption that gait inside a research laboratory does not differ from gait outdoors, when a participant is unaware of data collection in the latter. Means and interquartile ranges (IQR) of several spatio-temporal and kinematic gait characteristics were obtained from 19 young adults during several gait conditions both inside a laboratory environment and outdoors. Four comparisons were made between the two environments, including conditions involving: 1) self-selected speeds, 2) matching outdoors self-selected speeds, 3) matching outdoors self-selected speeds while carrying a crate, and 4) matching outdoors hurried speeds. Spatio-temporal variables differed between the two environments in that self-selected walking speed was 1.7% slower inside the lab and cadence was 1.4-2.6% lower for all four comparisons. At heel contact, the foot was 4.4-8.1% more dorsiflexed inside the lab for all comparisons except in matching hurried outdoors walking speed. Minimum toe clearance was 6.5-16.2% lower outdoors for all four comparisons. It is unclear if these differences impair the ability to generalize gait study results to outside the laboratory. Nevertheless, some specific differences exist in gait between environments, and that research should recognize.