Context: There is growing pressure to avoid hospitalizing emergency department patients who can be treated safely as outpatients, but this strategy depends on timely access to follow-up care. Objective: To determine the association between reported insurance status and access to follow-up appointments for serious conditions that are commonly identified during an emergency department visit. Design, Setting, and Participants: Eight research assistants called 499 randomly selected ambulatory clinics in 9 US cities (May 2002-February 2003) and identified themselves as new patients who had been seen in an emergency department and needed an urgent follow-up appointment (within 1 week) for 1 of 3 clinical vignettes (pneumonia, hypertension, or possible ectopic pregnancy). The same person called each clinic twice using the same clinical vignette but different insurance status. Main Outcome Measure: Proportion of callers who were offered an appointment within a week. Results: Of 499 clinics contacted in the final sample, 430 completed the study protocol. Four hundred six (47.2%) of 860 total callers and 277 (64.4%) of 430 privately insured callers were offered appointments within a week. Callers who claimed to have private insurance were more likely to receive appointments than those who claimed to have Medicaid coverage (63.6% [147/231] vs 34.2% [79/231]; difference, 29.4 percentage points; 95% confidence interval, 21.2-37.6; P<.001). Callers reporting private insurance coverage had higher appointment rates than callers who reported that they were uninsured but offered to pay $20 and arrange payment of the balance (65.3% [130/199] vs 25.1% [50/199]; difference, 40.2; 95% confidence interval, 31.4-49.1; P<.001). There were no differences in appointment rates between callers who claimed to have private insurance coverage and those who reportedly were uninsured but willing to pay cash for the entire visit fee (66.3% [132/199] vs 62.8% [125/199]; difference, 3.5; 95% confidence interval -3.7 to 10.8; P=.31). The median charge was $100 (range, $25-$600). Seventy-two percent of clinics did not attempt to determine the severity of the caller's condition. Conclusions: Reported insurance status is associated with access to timely follow-up ambulatory care for potentially serious conditions. Having private insurance and being willing to pay cash may not eliminate the difficulty in obtaining urgent follow-up appointments.