['In the 1990s, US welfare reform legislation imposed a 5-year lifetime limit on financial support for low-income families with young children (younger than 18 years). With increasing numbers of single mothers and their children reaching the end of their welfare eligibility, there is concern about potentially high rates of untreated psychiatric and substance use disorders in this population.', 'To determine the prevalence, correlates, and likelihood of treatment for mental and substance use disorders in a population of urban single mothers receiving Temporary Assistance for Needy Families (TANF).', 'In-person diagnostic assessments were conducted from November 1, 2003, to October 31, 2004.', 'Cook County, Illinois.', 'Female TANF recipients and residents of Cook County (N = 333) who were randomly sampled during the final 24 months of their eligibility for TANF.', "Prevalence rates of DSM-IV mental and substance use disorders using the World Health Organization's Composite International Diagnostic Interview.", 'Lifetime prevalence of Composite International Diagnostic Interview disorders was 61.0% (95% confidence interval [CI], 55.7%-66.3%); 12-month prevalence was 46.8% (41.5%-52.2%). Lifetime prevalence of mental disorders was 53.2% (95% CI, 47.8%-58.5%); 12-month prevalence was 44.1% (38.8%-49.5%). Lifetime prevalence of substance use disorders was 29.1% (95% CI, 23.9%-33.8%); 12-month prevalence was 9.0% (6.8%-12.0%). Lifetime prevalence of comorbid mental/substance use disorders was 21.3% (95% CI, 16.9%-25.7%); 12-month prevalence was 6.3% (3.7%-8.9%). Only 21.7% (95% CI, 14.8%-28.5%) of participants with 12-month mental disorders received treatment for mental disorders; 41.4% (22.3%-60.4%) of participants with 12-month substance abuse disorders received treatment for substance use disorders.'] Do prevalence of psychiatric and substance use disorders among single mothers nearing lifetime welfare eligibility limits?