Mobility in older adults is typically discussed in terms of component maneuvers including analysis of gait and postural instability; activities that depend on mobility such as bathing, dressing, or shopping; or adverse events during mobility such as falls or motor vehicle crashes. None of these approaches reflects a key aspect of mobility - the extent of movement within a person's environment, or life space in the gerantological literature. Here we describe this concept as in applies to mobility and present a questionnaire instrument designed to measure life space in community-dwelling older adults. Results indicate that the Life Space Questionnaire (LSQ) is reliable and has construct and criterion validity in a sample of older adults. The LSQ can be used to establish the spatial extent of an older person's mobility and may ultimately be useful as an outcome measure in studies evaluating interventions designed to enhance mobility and independence in community-dwelling older populations.