<br>        Inclusion Criteria:<br><br>          -  Children from birth to less than 6 months with documented symptomatic or asymptomatic<br>             venous or arterial thrombosis who have been treated with anticoagulant therapy for at<br>             least 5 days.<br><br>          -  Gestational age at birth of at least 37 weeks.<br><br>          -  Hemoglobin, platelets, creatinine, ALT and total and direct bilirubin assessed within<br>             10 days prior to enrollment.<br><br>          -  Oral feeding/nasogastric/gastric feeding for at least 10 days.<br><br>          -  Informed consent provided.<br><br>          -  Body weight >2600 g<br><br>        Exclusion Criteria:<br><br>          -  Active bleeding or high risk for bleeding contraindicating anticoagulant therapy,<br>             including history of intra-ventricular bleeding.<br><br>          -  Symptomatic progression of thrombosis during preceding anticoagulant treatment.<br><br>          -  Planned invasive procedures, including lumbar puncture and removal of non-peripherally<br>             placed central lines during study treatment.<br><br>          -  Hepatic disease which is associated with either: coagulopathy leading to a clinically<br>             relevant bleeding risk, or alanine aminotransferase (ALT) > 5x upper level of normal<br>             (ULN) or total bilirubin (TB) > 2x ULN with direct bilirubin > 20% of the total.<br><br>          -  Creatinine >1.5 times of normal.<br><br>          -  Uncontrolled Hypertension defined as >95th percentile.<br><br>          -  History of gastrointestinal disease or surgery associated with impaired absorption.<br><br>          -  Platelet count <100 x 109/L.<br><br>          -  Concomitant use of strong inhibitors of both cytochrome P450 isoenzyme 3A4 (CYP3A4)<br>             and P-glycoprotein (P-gp), e.g. all human immunodeficiency virus protease inhibitors<br>             and the following azole-antimycotics agents: ketoconazole, itraconazole, voriconazole,<br>             posaconazole, if used systemically (fluconazole is allowed)<br><br>          -  Concomitant use of strong inducers of CYP3A4, e.g. rifampicin, rifabutin,<br>             phenobarbital, phenytoin and carbamazepine<br><br>          -  Indication for anticoagulant therapy other than current thrombosis.<br><br>          -  Indication for antiplatelet therapy or non-steroid anti-inflammatory drug (NSAID)<br>             therapy. Incidental use is allowed.<br><br>          -  Hypersensitivity to rivaroxaban or its excipients.<br><br>          -  Participation in a study with an investigational drug or medical device within 30 days<br>             prior to enrollment.<br>