Summary. Background: Well known risk factors for upper extremity deep venous thrombosis are the presence of a central venous catheter (CVC) and malignancy, but other potential risk factors, such as surgery, injury and hormone replacement therapy (HRT), have not yet been explored. Methods: We performed a population-based case-control study including 179 consecutive patients, aged 18–70 years with upper extremity deep venous thrombosis and 2399 control subjects. Participants reported on acquired risk factors in a questionnaire and factor V Leiden and prothrombin 20210A mutation were ascertained. Information on CVC was obtained from discharge letters. Results: Forty-two patients (23%) and one control subject (0.04%) had a CVC (ORadj: 1136, 95% CI: 153–8448, adjusted for age and sex). Cancer patients without a CVC had an eightfold increased risk of venous thrombosis of the arm (ORcrude: 7.7, 95% CI: 4.6–13.0). Other evident risk factors were prothrombotic mutations, surgery, immobilization of the arm (plaster cast), oral contraceptive use and family history, with odds ratios varying from 2.0 up to 13.1. The risk in the presence of injury and during puerperium was twofold or more increased, although not significantly. In contrast HRT, unusual exercise, travel and obesity did not increase the risk. Hormone users had an increased risk in the presence of prothrombotic mutations or surgery. Obese persons (BMI > 30 kg m−2) undergoing surgery had a 23-fold increased risk of arm thrombosis compared with non-obese persons not undergoing surgery. Conclusion: A CVC is a very strong risk factor for arm thrombosis. Most risk factors for thrombosis in the leg are also risk factors for arm thrombosis.