Background: The U.S. poverty rate has increased since 2000, but the depth of poverty experienced by Americans has been inadequately studied. Of particular concern is whether severe poverty is increasing, a trend that would carry important public health implications. Methods: Income-to-poverty (I/P) ratios and income deficits/surpluses were examined for the 1990–2004 period. The severely poor, moderately poor, and near-poor were classified as those with I/P ratios of less than 0.5, 0.5 to 1.0, or 1.0 to 2.0, respectively. Income deficits/surpluses were classified relative to the poverty threshold as Tier I (deficit $8000 or more), Tier II (deficit or surplus less than $8000), or Tier III (surplus more than $8000). Odds ratios for severe poverty and Tier I were also calculated. Results: Severe poverty increased between 2000 and 2004—those with I/P ratios of less than 0.5 grew by 20%, and Tier I grew by 45% to 55%—while the prevalence of higher levels of income diminished. The population in severe poverty was over-represented by children (odds ratio [OR]=1.69, confidence interval [CI]=1.63–1.75), African Americans (OR=2.84, CI=2.74–2.95), and Hispanics (OR=1.64, CI=1.58–1.71). Conclusions: From 2000 to 2004, the prevalence of severe poverty increased sharply while the proportion of Americans in higher income tiers diminished. These trends have broad societal implications. Likely health consequences include a higher prevalence of chronic illnesses, more frequent and severe disease complications, and increased demands and costs for healthcare services. Adverse effects on children warrant special concern. The growth in the number of Americans living in poverty calls for the re-examination of policies enacted in recent years to foster economic progress. [Copyright &y& Elsevier]