PurposeSpontaneous muscle hematomas (SMH) are frequently seen in the Emergency Department (ED), particularly as a complication of anticoagulation treatments. To date, there are no standard guidelines for the management of this condition in the ED.This work aims to identify clinical-radiological parameters of SMH at risk of poor outcomes. MethodThis is a retrospective, observational cohort study conducted in an urban teaching hospital from 2016 to 2019. A multivariate logistic regression analysis was performed to identify parameters independently associated with an adverse outcome defined as the need for treatment (blood products, TAE, surgery) or hospitalization. The parameters analyzed were hematoma size, anticoagulation therapy, age, and the Charlson Comorbidity Index (CCI). ROC analysis was performed to identify the best cut-off hematoma size value to predict poor outcomes. ResultsOur study enrolled 231 patients aged between 18 and 96 years, with a mean age of 67 years. In our population, 125 patients (54.1 % %) were on anticoagulant therapy.Multivariate analysis showed that an SMH diameter > 5.5 cm was independently associated with poor outcome ((odds Ratio [95 % CI] 4,009 [1,786–9,001], p 0.001). Among clinical parameters, only advanced age was proved to be an independent predictor of adverse outcomes (odds Ratio [95 % CI] 1,035 [1,003–1,069], p = 0.033) ConclusionsOur data suggest that an SMH diameter greater than 5.5 cm on a CT scan and advanced age are predictors of poor outcomes. Surprisingly, anticoagulant therapy seems to play a minor role in the outcome of SMHs.