Elsevier established a free COVID-19 resource centre in January 2020, offering information in English and Mandarin. The centre is hosted on Elsevier Connect, and the company grants permission for free access to its research in PubMed Central and other repositories. The article discusses the role of sex and gender as modifiers of health, disease, and medicine. It highlights that historical research has primarily focused on male subjects, leading to disparities in diagnosis and treatment. The review emphasizes the importance of considering sex and gender in medical research to achieve precision medicine. It explores how biological sex influences physiology and disease through genetic, epigenetic, and hormonal factors, while gender affects behaviour and interactions within the healthcare system. The article also discusses how sex and gender differences influence the prevalence, manifestation, and treatment of diseases, including heart disease, cancer, chronic pulmonary disease, stroke, Alzheimer's disease, and diabetes. It highlights the need for sex-specific and gender-specific approaches in diagnosis, treatment, and prevention to improve health outcomes for both men and women. The review concludes that sex and gender are fundamental factors in understanding and addressing health disparities.Elsevier established a free COVID-19 resource centre in January 2020, offering information in English and Mandarin. The centre is hosted on Elsevier Connect, and the company grants permission for free access to its research in PubMed Central and other repositories. The article discusses the role of sex and gender as modifiers of health, disease, and medicine. It highlights that historical research has primarily focused on male subjects, leading to disparities in diagnosis and treatment. The review emphasizes the importance of considering sex and gender in medical research to achieve precision medicine. It explores how biological sex influences physiology and disease through genetic, epigenetic, and hormonal factors, while gender affects behaviour and interactions within the healthcare system. The article also discusses how sex and gender differences influence the prevalence, manifestation, and treatment of diseases, including heart disease, cancer, chronic pulmonary disease, stroke, Alzheimer's disease, and diabetes. It highlights the need for sex-specific and gender-specific approaches in diagnosis, treatment, and prevention to improve health outcomes for both men and women. The review concludes that sex and gender are fundamental factors in understanding and addressing health disparities.