A case-control study of primary lung cancer patients including 309 case (male 193, female 116) and 1,231 controls (male 768, female 463) was carried out in the monitored population for SINO-MONICA Project (WHO) during 1990-1993. This was a population based case-control study involved 0.75 million population in order to detect the relationship between lung cancer at preclinic stage and 6 psychosocial factors. There were 3 factors positively associated with lung cancer. They were 1) burst of "emotion and could not be controlled" (OR 1.82 P < 0.01), 2) "poor working circumstances" including poor relationship with colleagues (OR 1.37 P < 0.05) and superiors (OR 1.55 P < 0.01) and 3) the "depressive feeling for a long time" (OR 4.14 P < 0.01), when we considered "long standing depressive feeling" as a risk factor for lung cancer and calculated by an exposure rate of 8.8%, the population attributable risk percent (PAR%) would be 21.6% (male 18.7%, female 26.4%). Our findings suggested that the relationship between lung cancer at preclinic stage and psycho-social factor did exist.