BACKGROUND: There have been many reports of the adverse psychological effects of screening. Here we discuss the results of a randomized controlled study--one of the first to address this issue. AIM: To determine the extent to which participation in a population-based intervention programme that aims to reduce the risk of cardiovascular diseases raises concerns about health, or undermines a belief in the ability to reduce that risk. METHOD: A randomized controlled trial involving 13 general practices in England, Wales and Scotland was conducted. Two thousand, nine hundred and eighty-four middle-aged men and women undergoing cardiovascular risk-screening and intervention, and a randomized comparison group of 3,576 men and women from the same practices, who were not offered the intervention, were compared on three outcomes: perception of current health, perceived risk of suffering a heart attack, and perceived ability to reduce the risk of suffering a heart attack. RESULTS: We found no evidence to suggest that participation in this one-year, population-based intervention programme, to reduce the risk of cardiovascular disease raised concerns about health or risk of a heart attack; indeed, those in the intervention group were slightly more optimistic about their health. Alterations in perceptions of current health and the risk of suffering a heart attack were associated directly with true alterations in risk factors. A more noticeable effect on participants in this intervention programme was a reduction in their perceived ability to further reduce their risks of a heart attack. This was associated with a decrease in weight and with quitting smoking. CONCLUSION: Contemporary screening and intervention programmes in primary care, aimed at reducing risk of cardiovascular disease, do not necessarily lead to raised anxiety or concern about health. A more subtle effect of screening would appear to be one of reassurance in the face of continuing, albeit reduced, risk.