The Japan Nurses' Health Study (JNHS) is a prospective cohort investigation of the effects of lifestyle and healthcare on women's health. The study population comprises female registered nurse, licensed practical nurse, and midwife. The participants were recruited in cooperation with the Japanese Nursing Association and the Japan Menopause Society. The baseline survey was completed in 2007, and 49928 women responded from 47 prefectures of Japan. Approximately on third of the respondents agreed to be followed-up. Changes in lifestyle, healthcare, incidence of diseases, and health outcome over time are being studied. The cohort members received biennial follow-up questionnaires by mail.