This study aims to present the main results achieved in the regulation of health insurance plans through the National Agency of Supplementary Health, an agency set up to promote a balance in the relationship between health insurance plans and their consumers, making the health insurance market more efficient. As examples of the important progress achieved in regulating the sector, the authors emphasize: greater control of the inflow and outflow of service operators in the market; the widening of contractual coverage; monitoring and control of readjustments; encouragement of health promotion practices and increased training in the sector; grace period flexibility. Examples of regulatory gaps however, include: problems monitoring the quality of the care provided; tax breaks; the existence of discount cards; companies operating as health insurance plans without the ANS registration; the use of harmful mechanisms of assistance regulation by health insurance companies.