Inclusion Criteria:

1. Adult patients age ≥ 18 years old.
2. Objectively confirmed diagnosis within 14 days of an acute symptomatic SVT of the lower extremities by standardized CUS, where SVT is defined as incompressibility of a venous segment located along the course of a known superficial vein.
3. Anticoagulation for SVT is warranted per clinicians.
4. Able and willing to provide written informed consent.

Exclusion Criteria:

1. Other indication(s) for therapeutic or prophylactic dose anticoagulation (e.g. atrial fibrillation, mechanical valve, etc.).
2. History of PE or DVT within 6 months (180 days) of screening.
3. >5 days of any anticoagulants for the index SVT.
4. Requires use of aspirin >100mg daily or other antiplatelet agents.
5. Patients receiving concomitant systemic treatment with strong inhibitors of both CYP 3A4 and P-gp (e.g. cobicistat, ketoconazole, itraconazole, posaconazole, ritanovir, etc.).
6. Active bleeding or history of CRNMB or major bleeding (as defined by the ISTH) within 30 days of screening.
7. History of severe head trauma or ophthalmic, spinal, cerebral surgery within 90 days of screening.
8. Have acute endocarditis.
9. Thrombocytopenia (platelet count <50,000/uL), acute hepatitis, chronic active hepatitis, cirrhosis with severe hepatic impairment defined by a Childs-Pugh class B or C.
10. Creatinine clearance <30 ml/min.
11. Known contraindication to treatment with rivaroxaban.
12. Are participating in another interventional trial that would compromise the results or integrity of this trial as determined by the investigator.
13. Pregnant or breast feeding.
14. Known hereditary or acquired severe hemorrhagic disease.
15. Life expectancy <3 months.
16. Unstable medical or psychological condition that would interfere with trial participation at the discretion of the site investigator.