Objective: Long term incidence of symptomatic venous thromboembolism (VTE) and bleeding events in patients with superficial vein thrombosis (SVT) was investigated. Methods: In this prospective, observational study, patients with acute SVT were treated at the discretion of the responsible physician. The primary efficacy outcome was symptomatic VTE including deep vein thrombosis (DVT), pulmonary embolism (PE), and recurrent or extending SVT. The primary safety outcome was clinically relevant bleeding, recorded at periodic clinic visits over a 12 month period. Results: The mean age of 872 patients with 12 month follow up was 60.6 ± 14.5 years, 64.5% were female, 80.1% had chronic venous disease (defined as chronic venous insufficiency and or varicose veins), and 41.9% had a history of VTE. They were receiving fondaparinux in 62.1% (mean duration 34.9 ± 15.7 days), low molecular weight heparin (LMWH) in 25.0% (mean duration 26.2 ± 23.2 days), any other anticoagulants in 6.2%, and no anticoagulant in 6.7%. At 12 months, 108 patients (14.3%) achieved the primary efficacy outcome. The most common VTE event was recurrent or extending SVT in 11.0%, followed by symptomatic DVT in 2.7%, symptomatic PE in 2.4%, hospitalisation due to VTE in 1.8%, and death in 1.1%. Clinically relevant bleeding events occurred in 2.1% of patients, and major bleedings in 0.3%. By drug, the rate of the primary efficacy outcome was highest in the LMWH group (22.4%) and lowest in the fondaparinux group (10.4%). In a multivariable model, patients with events between three months and 12 months were significantly more likely to have higher BMI (hazard ratio [HR] 1.06; p =.002), history of VTE (HR 2.89; p =.002), and severe systemic infections (HR 7.59; p =.006). Conclusion: The risk of symptomatic VTE remained elevated over 12 months of follow up. Therefore, anticoagulation beyond 45 days may be considered in patients with risk factors. [ClinicalTrials.gov identifier: NCT02699151.]