Cancer and cardiovascular disease account for more than 60% of all deaths in Sweden, these alongside other serious illnesses such as diabetes and respiratory disease account for two thirds of deaths worldwide. Moreover, even in Sweden, with universal access to healthcare, socioeconomic inequalities in incidence and survival from serious illness exist. Lifestyle factors associated with socioeconomic position, such as diet, physical activity, and smoking, influence the risk of several serious illnesses and survival after disease occurrence. However, previous studies often only measure lifestyle and socioeconomic factors at one point in time. As such, they do not answer the clinically important questions of whether patients can improve their prognosis by changing their lifestyle after a serious disease diagnosis. Few studies have tried to identify determinants of different patterns of lifestyle and socioeconomic factors. A more complete overview of mechanisms linking lifestyle and socioeconomic factors to ill health and will highlight vulnerable groups and traits that can be targeted in future interventions. Insight from a life-course perspective, will allow future interventions to be appropriately targeted to have maximum impact for health at a population level. Given the clinical and public health relevance of the issues described, these topics merit further research. The aims of this research program are: 1) To increase knowledge of patterns and determinants of (change in) lifestyle and socioeconomic factors before and after a serious illness 2) To examine (change in) lifestyle and socioeconomic factors before and after a serious illness in relation to disease incidence, long-term outcomes, survival and socioeconomic factors, and 3) To better understand the broader mechanisms relating to these association and how these associations have changed over time The research program will primarily be conducted using Swedish national register data, which may be complemented by data from other large databases and cohort studies. The Swedish national registers contain information on socioeconomic and sociodemographic variables, lifestyle variables, and health variables for individuals in Sweden across their life-course. Moreover, information can be linked across generations to include aspects of individual’s wide social context. Analyses will focus on serious illnesses that contribute a large burden of ill health in Sweden, this will include cancer (all types combined as well lung, colorectal, prostate and female breast cancers separately, since these are the four largest contributors to cancer related mortality in Sweden), stroke, myocardial infarction, diabetes and proxy measures of serious illness, such as hospitalisation. This work will inform the development of interventions and clinical and public health guidelines aiming to support individuals at risk of serious illness and patients after diagnosis of serious illness, identify target populations who may particularly benefit from such interventions and guidelines, and lead to strategies to reduce socioeconomic inequalities in risk and consequences of serious illness. In addition, it will allow clinicians to offer evidence-based advice to their patients regarding whether or not changing habits of a lifetime can influence survival. Moreover, it will help patients make informed decisions about their lifestyle following a diagnosis of serious illness.