This study examines nursing home regulatory activity by the states, assesses interstate variations in the volume and severity of nursing home deficiencies, and explores state-level factors that may account for these differences. Nursing home deficiency citation data over a 5-year period (2000-2004) were obtained from the Centers for Medicare and Medicaid Services. We examined interstate variations in regulatory activity and identified predictors of deficiency volume and severity at the state level (demographics, elected officials, industry characteristics, etc.) using the linear mixed model. Deficiency volume remained stable across the 50 states from 2000 to 2004, while deficiency severity decreased significantly. California had the highest volume of deficiencies per nursing home; Wisconsin had the lowest. New Hampshire had the highest percentage of severe deficiencies; California had the lowest. Higher deficiency volume was found in states with lower median household income, a lower proportion of residents aged 85 and older, and a Democratic legislature. Higher deficiency severity was associated with higher median household income and a higher proportion of Medicaid nursing home residents in a state. In contrast, greater state agency funding, higher state standards for nursing home administrators, and a Democratic and more professional legislature predicted lower deficiency severity. Nursing home residents in the United States receive unequal protection from abuse and neglect, and this is partly due to their state of residence. Interstate variations in deficiency volume and severity are due to a complex set of factors beyond nursing home quality. © 2008 by The Haworth Press. All rights reserved.