OBJECTIVES: To identify the most used way to make complaints about health plans to The Federal Regulatory Agency for Private Health Insurance and Plans (ANS) in Brazil.  METHODS: A retrospective analysis of data was done to identify the most used channel of the three currently available: the personal, the call center and the electronic. Two different periods were considered to the study: the second semester of 2013 (the last one that still used an institutional email to the electronic complaints) and the second semester of 2014 (after the creation of a specific form for complaints available on ANS website).  RESULTS: According to the data, the way most consumers choose to make a complaint is the call center (68,5% -2013 and  71,7%-2014). The second one is the electronic way. Comparing the two periods of the study it’s possible to note a decrease of 5% in the use of electronic complaints after the form implementation (26% to 21%). The less used way is the personal one (6, 7% -2013 5,4%-2014). The study doesn’t point a clear relationship between the themes of the complaints and the kind of service used. CONCLUSIONS: The study showed the call center is the primary service used. The personal service is less used then the others, probably because it's offered only in the biggest Brazilian cities. The implementation of the electronic form, through which the consumer can register and track their complaints, didn’t increase the use of this channel. It's possible that form design, with required fields and limited number of characters, is acting like a complicating factor. As is known, the excessive work of the call center can compromise its quality and efficiency. So, it would be interesting to verify the key points to improve the electronic form to spread its use aiming to reduce costs through a future staff downsizing.