We developed the Nursing Home Life-Space Diameter (NHLSD) as a measure of the extent and frequency of mobility among skilled nursing facility (SNF) residents. Intrarater and interrater reliability was assessed in a small sample of SNF residents. The means and ranges of NHLSD scores, the characteristics associated with NHLSD score, and the association between NHLSD score and other functional characteristics were then determined among 398 residents of 12 SNFs. NHLSD scores ranged from 0, signifying bed- or chair-bound to 50, signifying leaving the facility daily. The correlation between NHLSD scores by two nurses was 0.951; the correlation between scores at two points of time was 0.922. Mean score among the 398 subjects was 27.05. Decreased vision, presence of a neurologic disease, and arthritis were all associated with lower NHLSD score. Mobility (NHLSD) score was moderately correlated with other functional characteristics such as participation in social activities (Spearman's correlation = +0.565). The NHLSD, which represents a simple and reliable assessment of mobility among SNF residents, could be used to assess the effect of interventions and to monitor changes among SNF residents.