Background A well-functioning primary care system has the capacity to provide effective care for patients to avoid nonurgent emergency department (ED) use and related costs. Objective This study examined how patients' perceived deficiency in ambulatory care is associated with nonurgent ED care costs nationwide. Methods This retrospective cohort study used data from the 2010-2011 Medical Expenditure Panel Survey. This study chose usual source of care, convenience of needed medical care, and patient evaluation of care quality as the main independent variables. The marginal effect following a multivariate logit model was employed to analyze the urgent vs. nonurgent ED care costs in 2011, after controlling for covariates in 2010. The endogeneity was accounted for by the time lag effect and controlling for education levels. Sample weights and variance were adjusted with the survey procedures to make results nationally representative. Results Patient-perceived poor and intermediate levels of primary care quality had higher odds of nonurgent ED care costs (odds ratio [OR] = 2.22, p = 0.035, and OR = 2.05, p = 0.011, respectively) compared to high-quality care, with a marginal effect (at means) of 13.0% and 11.5% higher predicted probability of nonurgent ED care costs. Costs related to these ambulatory care quality deficiencies amounted to $229 million for private plans (95% confidence interval [CI] $100 million-$358 million), $58.5 million for public plans (95% CI $33.9 million-$83.1 million), and an overall of $379 million (95% CI $229 million-$529 million) nationally. Conclusions These findings highlight the improvement in ambulatory care quality as the potential target area to effectively reduce nonurgent ED care costs.