Aim: Pulmonary embolism (PE) is a life-threatening condition that requires early diagnosis and treatment. There is still a need for precise and non-invasive biomarkers that can be used to diagnose PE. This study aimed to determine the diagnostic value of Cardiotrophin-1 (CT-1) in patients with acute PE and ascertain the relationship between serum CT-1 level and disease prognosis and severity. Materials and Methods: In this prospective study, the serum CT-1 levels of 165 patients with suspected acute PE were measured. The patients were divided into two groups, PE (+) and PE (−), based on their computed tomography angiography results. Their serum CT-1 levels were compared.Results: The CT-1 levels of the PE (+) group (median=4.18 pg/mL, range=3.57-9.55 pg/mL) was non-significantly (p=0.08) different from those of the PE (−) group (median=4.38 pg/mL, range=3.57-51.64 pg/mL). Based on the severity of the condition, there were significant differences (p=0.001) in the CT-1 levels of the patients in the intermediate-low risk group (median=4.19 pg/mL, range=3.62-5.32 pg/mL), intermediate-high risk group (median=4.06 pg/mL, range=3.57-9.31 pg/mL) and high risk group (median=5.01 pg/mL, range=3.89-9.55 pg/mL). Based on the clinical course, the CT-1 levels of the patients in the good clinical course group (median=4.15 pg/mL, range=3.57-9.31 pg/ml) were significantly different (p=0.004) from those in the poor clinical course group (median=4.53 pg/mL, range=3.66-9.55 pg/mL).Conclusion: CT-1 level was not observed to be a precise biomarker for the diagnosis of acute PE. However, our study demonstrated that the serum CT-1 levels can be used as a biomarker for ascertaining the severity and prognosis of patients with PE.