The overall aim of screening is to reduce the burden of the disease including incidence of disease, and disease related morbidity or mortality. An evaluation of any screening programme must consider the likely harms as well as the benefits of such a programme. Screening tests can be used to identify early disease; such as in breast cancer screening, or a pre-disease abnormality such as in cervical and bowel cancer screening. Screening for disease and pre-disease abnormities is the most common type of screening. However, screening for markers and using this information to give personalised risk information is becoming increasingly common. For example, the NHS health checks which use markers such as blood pressure and cholesterol to communicate an individualsâ risk of cardiovascular disease. Screening for early disease or pre-disease abnormality is in many ways very different to testing future disease risk and for this reason, they can impact a personâs behaviour very differently. Screening for the presence of disease has been identified as causing âfalse reassuranceâ whereby those who receive a negative screening test result, interpret their result as indicating they are less likely to develop the disease in the future. This is a misconception as screening only identifies if a person currently has or doesn't have the condition or marker for the condition at the time of screening and cannot provide information about a personâs future risk of developing the disease. As a result, some argue that screening for disease may have a negative impact on participantsâ lifestyle behaviours e.g exercising, smoking, drinking alcohol. Testing for markers of disease and providing personalised disease risk information is generally perceived to increase motivation to change related behaviours, though there is little data to support this. It is important to consider how screening for disease and for risk of disease can impact on participantsâ lifestyle behaviours and choices as changing these has the potential to reduce the risk of many diseases. This research aims to answer the question âDo negative screening test results cause false reassurance?â by reviewing the currently available evidence from randomised screening trials. It also aims to discover through the analysis of a feasibility study if personalised disease risk increases uptake and adherence to a weight loss and lifestyle programme amongst women in the NHS national breast screening programme. Taken together these two studies provide information on the likely harms and benefits of the two approaches to screening. Overall this thesis demonstrates that false reassurance as a result of negative screening is unlikely to be a significant issue. It also demonstrates that being at increased risk of disease may increase uptake to a weight loss and lifestyle programme. However, despite increased motivation from higher risk groups to join, additional risk information did not affect adherence to the programme.