Policymakers in England are increasingly encouraging the formation of 'large-scale' general practice provider collaborations with the expectation that this will help deliver better quality services and generate economies of scale. However, solid evidence that these expectations will be met is limited. This paper reviews evidence from other inter-organisational healthcare collaborations with similarities in their development or anticipated impact to identify lessons. Medline. SSCI, Embase and HMIC database searches identified a range of initiatives which could provide transferable evidence. Iterative searching was undertaken to identify further relevant evidence. Thematic analysis was used to identify areas to consider in the development of large-scale general practice providers. Framework analysis was used to identify challenges which may affect the ability of such providers to achieve their anticipated impact. A narrative approach was used to synthesise the evidence. Trade-offs exist in 'scaling-up' between mandated and voluntary collaboration; networks versus single organisations; small versus large collaborations; and different types of governance structures in terms of sustainability and performance. While positive impact seems plausible, evidence suggests that it is not a given that clinical outcomes or patient experience will improve, nor that cost savings will be achieved as a result of increasing organisational size. Since the impact and potential unintended consequences are not yet clear, it would be advisable for policymakers to move with caution, and be informed by ongoing evaluation.