Background: Cancer and its treatment can severely affect sexual health. It is unknown how this may relate to the feelings of closeness between patients and their partners. Aim: To assess the association between sexual health and closeness in the relationship in couples coping with advanced cancer. Design: This study was part of a prospective multicentre longitudinal observational cohort study on experienced quality of care and quality of life in patients with advanced cancer and their relatives (eQuiPe). Setting/participants: Baseline data regarding sexual health and closeness in people with advanced cancer and their partners. Results: Out of the 566 dyads, 14 were same-sex couples. Especially male partners showed an interest in sex, but more than half of all patients and partners were not sexually active. Approximately one third experienced sexual dysfunction to be a problem but did not seek specialized support (<10%). There was a positive association between own sexual satisfaction and feelings of closeness in the relationship, which was stronger for partners compared to patients ( p < 0.001). Sexual satisfaction of the other person was also related to own feelings of closeness ( p = 0.003). Conclusions: Couples coping with advanced cancer clearly face challenges regarding sexual health but are not likely to seek specialized support. When discussing sexual health, it is crucial that health care professionals pay attention to the aspects of sexual health that may contribute to feeling close to each other and suggest specialized care if necessary. Trial registration: The eQuiPe study is registered as NTR6584 in the Netherlands Trial Register.