Background: This review explores factors sustaining and threatening couples' relationships when both have advanced illness. Methods: Qualitative studies exploring relationships between two people in a marriage/partnership with advanced illness are included. Findings: A total of 12 articles are included. Internal enabling factors, external enabling factors and threatening factors are identified. However, there is limited evidence internationally on factors sustaining these relationships and crisis factors. Little is known about the impact of crises on couples and the process of change from mutual dependency to carer and cared for. Conclusions: The article concludes that shifts by services towards holistic care focused on the couple's needs are indicated.