OBJECTIVE: To explore general practitioners' (GPs') experiences of cooperation with hospital-based physicians regarding multimorbid patients and to identify challenges as well as strategies in managing such challenges. Study setting: Three medical practices in a provincial town in Denmark.STUDY DESIGN: A qualitative methodological design was used with explorative data collection among GPs. Data collection/Extraction methods: Participant observation, qualitative interviews and a focus group interview were conducted. Interpretive description was used as the analytical framework. Principal findings: The GPs appreciated cooperating with physicians in optimizing treatment of multimorbid patients. However, three main challenges were experienced: insufficient communication and coordination; unclear divisions of roles and responsibilities; and differences in the way of approaching patients. The GPs navigated these challenges and complexities by taking advantage of their personal relationships and by developing creative and patient-centred ad hoc solutions to difficulties in cross-sectorial cooperation. A hospital initiative to support care for multimorbid patients has not been adopted by the GPs as a preferred strategy.CONCLUSIONS: The structures of the health care system severely challenged cooperation regarding multimorbid patients; nevertheless, these GPs were aware of the advantages of cooperation, and their mainstay strategy in this involved personalized solutions and flexibility.