Objective To examine trends in the proportion of work‐related emergency department visits not expected to be paid by workers' compensation during 2003–2006, and to identify demographic and clinical correlates of such visits. Data Source A total of 3,881 work‐related emergency department visit records drawn from the 2003–2006 National Hospital Ambulatory Medical Care Surveys. Study Design Secondary, cross‐sectional analyses of work‐related emergency department visit data were performed. Odds ratios and 95 percent confidence intervals were modeled using logistic regression. Principal Findings A substantial and increasing proportion of work‐related emergency department visits in the United States were not expected to be paid by workers' compensation. Private insurance, Medicaid, Medicare, and workers themselves were expected to pay for 40 percent of the work‐related emergency department visits with this percentage increasing annually. Work‐related visits by blacks, in the South, to for‐profit hospitals and for work‐related illnesses were all more likely not to be paid by workers' compensation. Conclusions Emergency department‐based surveillance and research that determine work‐relatedness on the basis of expected payment by workers' compensation systematically underestimate the occurrence of occupational illness and injury. This has important methodological and policy implications.