Objectives: Little is known regarding the clinical features and course of in situ pulmonary artery thrombosis (PAT). The aim of the present study was to investigate the clinical characteristics of PAT. Methods: Patients with PAT were retrospectively identified from a tertiary referral center in South Korea. A control group consisted of patients with pulmonary embolism (PE) in whom the right or left pulmonary artery was the largest PE-involved site. We compared various clinical parameters between the two groups. Results: Of 23 PAT patients, the most common underlying condition was tuberculosis (TB)-destroyed lung (11 [47.8%]), followed by pulmonary artery stump after lobectomy or pneumonectomy (7 [30.4%]). In all patients except one, PAT was located in the right or left pulmonary artery. Computed tomography scans demonstrated that clots were completely or partially resolved less frequently in the PAT group than in the control group (4 [25%] versus 62 [90%], p<0.001). In the PAT group, three of seven patients (43%) who had undergone anticoagulation therapy exhibited improvement, and one of nine (11%) who had not received anticoagulation therapy experienced improvement; however, the difference was not significant. Conclusions: TB-destroyed lung was the most common underlying condition in Korean PAT patients, followed by pulmonary artery stump after lung resection. The clots in patients with PAT were mostly located in the right or left pulmonary artery, and clot resolution was less frequent in the PAT group compared to the PE group.