To assess which are the most important perceived influential factors on health among the Spanish adult population. This may provide sufficient information to promote primary health care campaigns directed specifically to those that acknowledge that lifestyles are important in spite of not living healthy lifestyles themselves.Observational cross-sectional study.Spain (Canary Islands not included).A representative sample of 1000 Spanish participants over 15 years old selected by a multistage procedure.Survey to evaluate the population choosing one of nine known health-related factors (smoking, food, alcohol intake, stress, physical activity, environment, body weight, support from family, genetics) as being one of the two most important factors influencing health through a validated questionnaire.The chi-square test for linear trend was used to assess the influence of factors coded on an ordinal scale. The Pearson chi-square test was applied for categorical factors. Smoking was considered the most influential health-related factor by most participants (47.8%). Males, those from lower socioeconomic and educational levels; people living in the south of Spain, and rural regions; those married and individuals who had 3 or more children below 15 years, perceived smoking more often as one of the most important determinants of health.These data suggest that a large percentage of the Spanish adult population recognizes that life-styles are important determinants of health.