Aspirin is an effective means to prevent recurrence and death in patients with vascular disease. However, the extent to which patients are aware of this is not known. The objective of the study was to compare the use and knowledge of prophylactic aspirin between patients on repeat cardiovascular drug prescriptions and their matched controls. A cross-sectional survey of 600 patients was carried out in a group general practice. The subjects included 200 patients on repeat cardiovascular drug prescriptions (vascular group), and two age–sex matched groups: patients on other repeat prescriptions (nonvascular group) and patients not on repeat prescriptions (control group), sampled from the practice register. Use and knowledge of prophylactic aspirin were the main outcome measures. Aspirin knowledge was 72% in the vascular group; 53% in the nonvascular group, and 58% in the control group. Apart from patients who reported possible contra-indications to aspirin, 77% of patients with repeat cardiovascular drug prescriptions reported using aspirin regularly compared with 16% and 9% in the nonvascular and control groups, respectively. Amongst patients on repeat cardiovascular drug prescriptions, aspirin knowledge was the strongest predictor of aspirin use. To conclude, use of prophylactic aspirin in one practice was appropriate and had overcome the usual socio-demographic barriers to preventive activity. However, there were still significant numbers not using it. Increased usage in patients with vascular disease could be achieved by improving public knowledge of the benefits of prophylactic aspirin.