Red cell distribution width (RDW) is strongly associated with prognosis in cardiopulmonary disorders such as coronary artery disease, acute myocardial infarction, acute and chronic heart failure, and pulmonary hypertension. However, its prognostic significance in acute pulmonary embolism (PE) is unknown. The aim of this study was to investigate the relation between admission RDW and early mortality in patients with acute PE. One hundred sixty-five patients with confirmed acute PE were included. Patients with previous treatment for anemia, malignancy, or chronic liver disease, those with dialysis treatment for chronic renal failure, and those who received erythrocyte suspension for any reason were excluded. A total of 136 consecutive patients with acute PE were evaluated prospectively. According to receiver-operating characteristic curve analysis, the optimal cut-off value of RDW to predict early mortality was >14.6%, with 95.2% sensitivity and 53% specificity. Patients were categorized prospectively as having unchanged (group 1) or increased (group 2) RDW on the basis of a cut-off value of 14.6%. The mean age of patients was 63 ± 15 years. The mean follow-up duration was 11 ± 7 days, and 21 patients died. Among these 21 patients, 1 (1.6%) was in group 1 and 20 (27%) were in group 2 (p <0.001). Increased RDW >14.6% on admission, age, presence of shock, heart rate, oxygen saturation, and creatinine level were found to have prognostic significance in univariate Cox proportional-hazards analysis. Only increased RDW >14.6% on admission (hazard ratio 15.465, p = 0.012) and the presence of shock (hazard ratio 9.354, p <0.001) remained associated with increased risk for acute PE-related early mortality in a multivariate Cox proportional-hazards model. In conclusion, high RDW was associated with worse hemodynamic parameters, and RDW seems to aid in the risk stratification of patients with acute PE.