The Danish Nurse Cohort is a longitudinal study that focuses on nurses' health. Inspired by the US Nurses’ Health Study,1 the Danish Nurse Cohort was initiated to examine the benefits and risks associated with hormone replacement therapy (HRT) in a European population. Thus, the original cohort outlined aims to further investigate the association between HRT use and the risk of (i) breast cancer, (ii) heart diseases and (iii) osteoporotic fractures.2 In 1990, the Danish Nurse Organization (DNO) authorized access to their membership register, enabling contact with Danish nurses. The register comprises active, inactive and retired nurses, as well as nursing students. As of 1 January 2024, it possesses a membership rate of >80% in the Danish Nurses Organization, encompassing >75% of currently employed Danish nurses. In 1993, a questionnaire was mailed to 23 170 female Danish nurses aged ≥44 years and 86.9% responded. In 1999, all DNO members age >44 years were reinvited. Of the 31 642 female nurses who were contacted, 76% responded. Since HRT was the focus of the baseline study, participation was limited to women who were aged ≥44 years. The cohort has had five waves of data collection: 1993, 1999, 2009, 2021 and 2024. Of the 15 322 female nurses who replied in both 1993 and 1999, a total of 12 955 nurses were still alive and residing in Denmark in 2009 and, of these, 11 114 (85.8%) completed the questionnaire (Table 1). In 2021 and 2024, all DNO members (including males) were invited to participate, with 36 658 (46%) responding in 2021 and 28 359 (39%) in 2024. Notably, 897 female nurses have participated in every wave from 1993 to 2024, whereas 1103 took part in the first four waves.