Very few studies have examined the impact of genetic testing for thrombophilia on health behaviours, perceptions of control over risk factors for venous thromboembolism, or health services utilization. Through a postal questionnaire we compared first degree relatives with thrombophilia (carriers) most of whom had received counseling, to those without (non-carriers) with respect to: (a) perceived causes of venous thromboembolism; (b) perceived control; (c) health behaviour changes; and (d) use of health care services. 44/51 for carriers and 26/47 for non-carriers completed questionnaires. Carriers were more likely to believe their risk of venous thromboembolism ‘is a little higher’ or ‘much higher’ than average (p < 0.001) but some continued to believe their risk ‘is the same as’ or ‘lower than’ average. 16%–32% of carriers did not recognize major risk factors. Stress, worry, or depression, negative attitude, and over-exertion were over-interpreted as risks. 37.2% did not appreciate that thrombophilia increases risk. Behaviour changes were uncommon. There is a need for research on education and strategies to improve knowledge in thrombophilia carriers.