The incidence of both venous and arterial thrombosis increases exponentially with age in both men and women. Possible reasons include: increasing immobility, trauma, surgery and acute medical illness; increasing prevalence (and/or cumulative effects) of obesity, raised blood pressure, dyslipidaemia and glucose intolerance; increasing prevalence of atherosclerosis; and increasing circulating markers of inflammation (C-reactive protein, CRP) and thrombosis. While arterial thrombosis is less common in women, the relative risk for classical risk factors associated with myocardial infarction is at least as strong in women as in men, in prospective population-based studies using MONICA criteria (e.g. Scottish Heart Health Study, Reykjavik Study). Some of these risk factors (e.g. smoking, cholesterol, triglycerides) show decreasing hazard ratios with age. Ongoing studies of newer potential risk factors for venous and arterial thrombosis (e.g. homocysteine, haemostatic and inflammatory variables) should elucidate their roles in risk prediction, including thrombotic risks of sex hormones which have effects on these variables.