OBJECTIVES: To determine the prevalence in out-patients of risk factors leading to venous thromboembolic disease (VTE); and to analyse what perception primary care centre (PCC) doctors have of this risk and what attitude they adopt to therapy. DESIGN: 1) An observational, crossover study, with patients included at random. 2) A study with a teaching intervention, which was neither controlled nor randomised. PATIENTS: PCC patients over 25 seen either on demand, with appointments or at home. INTERVENTION: A clinical history was composed, using a closed questionnaire. A risk category and therapeutic attitude were then assigned. A guide on prevention and treatment of VTD was presented and discussed in clinical sessions. RESULTS: 11 PCC doctors polled 272 patients. 45 of these had moderate to high risk of VTD; and 4 had one of the criteria of the European Accord on VTD prevention for commencing prophylactic treatment. In two of these four, it was thought necessary to start prophylaxis. CONCLUSIONS: The prevalence of patients with moderate to high risk of VTD is 17% in patients over 25 who seek medical attention at PCCs. Doctors detected 50% of moderate to high risk patients. If the criteria used for in-patients were followed, prophylaxis should have been started in 1.5% of patients.