In health care systems based upon managed competition, insurers are expected to negotiate with providers about price and quality of care. The Dutch experience, however, shows that quality plays a limited role in insurer–provider negotiations. It has been suggested that this is partly due to a lack of cooperation among insurers. This raises the question whether cooperation amongst insurers is a precondition or a substitute for quality-based competition. To answer this question, we mapped insurers' cooperating activities to enhance quality of care using a six-stage continuum. The first three stages (defining, designing and measuring quality indicators) may enhance competition, whereas the next three stages (setting benchmarks, steering patients and selective contracting) may reduce it. We investigated which types of insurer cooperation currently take place in the Netherlands. Additionally, we organized focus groups among insurers, providers and other stakeholders to examine their perceptions on insurer cooperation. We find that all stakeholders see advantages of cooperation amongst insurers in the first stages of the continuum and sometimes cooperate in this domain. Cooperation in the next stages is almost absent and more controversial because without adequate quality information, it is difficult to assess whether the benefits outweigh the cost associated with reduced competition.