There is a broad literature on the consequences of applying different welfare standards in merger control. Specific aspects of health care mergers, however, have not yet been considered. Two features of the health care sector are especially relevant. First, health care providers are possi-bly not profit oriented. Second, consumers can be covered by a mandatory health insurance and pay uniform premiums. The fact and level of payment is not connected to the consumption of health care services, which makes the concept consumer in merger control ambiguous. Previous literature on welfare standards in merger control has often built on the general result that consumer welfare is a more restrictive standard than total welfare. We model mergers on hospital markets and allow for non-profit maximizing behavior of providers and mandatory health insurance. We show that applying a restricted interpretation of consumer in health care merger control can reverse the relation between the two standards. Consumer welfare standard can be weaker than total welfare. Consequently, applying the wrong standard can lead to both clearing socially undesirable and to blocking socially desirable mergers. The possible negative consequences of applying a simple consumer welfare standard in merger control can be even stronger when hospitals maximize quality and put less weight on financial considerations. We also relate these results to the current practice of merger control.