This study assessed the association of multiple myeloma (MM) with age, body mass index (BMI, kg/m(2)), physical activity, occupational history, and medical history for a Japanese cohort of 46,157 men and 63,541 women aged 40-79 years followed during 1988-2003 years. Cox proportional hazard model was mainly used to estimate the age and sex adjusted hazard ratio (HR) of MM including 95% confidence interval (CI) for both sexes. Same model, adjusted for age, was also used for each sex. In total, 98 MM deaths (men=49 and women=49) was observed for both sexes. Higher age groups (60-69 and 70-79 years) experienced significantly higher unadjusted HR of MM than the age group of 40-49 years. Men revealed significantly higher age-adjusted MM than women (HR=1.5; 95% CI=1.0-2.2). For both sexes, higher BMI of >or=30 kg/m(2)) (HR=2.8; 95% CI=1.0-7.7), walking <or=30 minutes/day (HR=2.0; 95% CI=1.2-3.4), worried about personal relationship in working place (HR=2.3; 95% CI=1.3-4.2), restricted own pace in working place (HR=1.9; 95% CI=1.0-3.4), and history of peptic ulcer (HR=1.7; 95% CI=1.0-2.7) significantly increased age and sex adjusted MM risk. Some of the above-mentioned significant associations became insignificant for age adjusted sex specific analyses. However, these findings should be validated by further epidemiologic studies in Japan before generalization.