Medical management is commonly used among women with early pregnancy failure. The purpose of our study was to evaluate uterine content sonographic measurements for predicting medical management failure in early pregnancy loss. We conducted a retrospective cohort study in a university-affiliated hospital center including all women discharged from the emergency department (ED) with a diagnosis of early pregnancy failure who had medical management with misoprostol between 2011 and 2013. Only women with sonograms available for review were included in our study. All images were reviewed and the following cavity measurements, excluding the endometrial lining, were measured: cavity anteroposterior distance, cavity longitudinal distance, cavity transverse distance, and cavity volume. Logistic regression analysis was used to identify measurements that were independently associated with a subsequent need for dilation and curettage (D&C) and an unplanned return to the ED. Among 823 women presenting to the ED with first-trimester bleeding, 227 met inclusion criteria. Of all measurements evaluated, the cavity anteroposterior distance was found to be independently associated with D&C and an unplanned return to the ED. When a cavity anteroposterior distance cutoff of 15 mm was used, women were more likely to require D&C (adjusted odds ratio, 2.65; 95% confidence interval, 1.31-5.36; P< .01) and to have an unplanned return to the ED (adjusted odds ratio, 2.59; 95% confidence interval, 1.41-4.79; P < .01). In women with a cavity anteroposterior distance of less than 15 mm, 87.1% had successful medical management of early pregnancy loss, and 80.0% did not require an unplanned return to the ED. Although there is a need for further validation, patients identified as having a cavity anteroposterior distance of less than 15 mm should be considered good candidates for successful medical management.