Objective: To explain the global quality of life (QOL) from 2000 indicators representing all aspects of life. Design and setting: Two cross sectional population studies, one prospective cohort study and one retrospective cohort study. Participants: (1) Representative sample of 2500 Danes (18-88 years), (2) 7222 members of the Copenhagen Perinatal Birth Cohort 1959-1961 (31-33 years), (3) 9.006 mothers and their 8820 children born in Copenhagen 1959-1961, (4) 746 Danes (55-66 years). Main outcome measures: Global QOL measured by SEQOL (self evaluation of QOL) containing eight global QOL measures: Well-being, life-satisfaction, happiness, fulfilment of needs, experience of temporal and spatial domains, expression of life's potentials and objective factors. Results: 2000 associations; strongest between QOL and health, ability, the personal philosophy of life, the relationships to oneself, the partner and friends; weakest between QOL and 1000 early life factors, 1000 life events and 100 objective factors like income. Conclusions: Quality of life is associated with personal health and attitude towards life, rather than objective factors, life style, or life events. We conclude that QOL can be developed independently and thus be used as medicine.