Abstract Background People with multimorbidity are often seen in many different specialist health services, resulting in fragmented care. Conventional services are designed around specialties based on anatomical systems, rather than diseases that occur together. We examined whether organising services around clusters of co-occurring diseases would lead to fewer interactions with unique services and so improve integrated care. Methods We used the Clinical Practice Research Datalink, a nationally representative sample of primary care data in England, including all patients registered on 1st January 2015 with multimorbidity (two or more of 212 long-term conditions (LTCs)). We used the assignment of 212 LTCs to 15 clusters of co-occurring diseases, derived from our earlier work. For each patient, we calculated the number of interactions with different specialists, under both the existing specialty-based model, and the hypothetical cluster-based model, under the assumption that a patient required review for each LTC. Results Of 6,200,973 patients with multimorbidity, the mean age was 53 years, with a median (interquartile range) of 8 (5 - 11) LTCs per person. There was considerable variation in the assignment of diseases comparing 15 clusters versus 15 specialties. Under the existing model, 409,708 (6.6%) patients interacted with only one specialty, and under the hypothetical cluster model, 584,446 (9.4%) patients interacted with only one cluster. On average, patients interacted with 3.66 specialties versus 3.30 hypothetical clusters (p < 0.001 for difference). Conclusions Health services designed around clusters of co-occurring diseases might lead patients to interact with fewer different services and so experience less fragmented care. Further work is needed to understand which specialties collaborating, and how, would have the greatest impact on improving integrated care. Key messages • Health services designed around clusters of co-occurring diseases led to a small reduction in the number of interactions with different services per year. • Designing services around clusters of co-occurring diseases might reduce fragmented care for people with multimorbidity.