Hospital planning in New York has been since the 1930s an intensely political process with high stakes. The leaders of Blue Cross and their allies used the hospital planning process in the city and the state as a means to extend and protect corporate authority in what they took to be the public interest. When Blue Cross was established in the 1930s, its leaders used the mechanisms of formal planning as part of their solution to pressing problems in the organization and distribution of hospital services. In the decade after World War II, Blue Cross had an immense impact on hospital planning in New York as a result of its growth and its underwriting policies. Conflicts between Blue Cross and state regulators beginning in the 1950s led to a new formulation of the politics of planning. Blue Cross became a partner with the state in regulating hospitals. The state and Blue Cross behaved as co-regulators until the 1980s. The interpretation in this paper revises the earlier accounts of health politics in New York by Law (1976) and Alford (1975).