The quality of health information available on the Internet has proved difficult to assess objectively. The Internet's growing popularity as a source of health information, accompanied by the lack of regulation of websites, has resulted in research that has developed and tested tools to evaluate health website quality. However, only a few studies have tested the validity and reliability of these tools. There is a lack of consensus about appropriate indicators with which to operationalize the concept of quality health information. This study aimed to contribute to this research by testing the validity and reliability of existing tools, through their application to websites that provided information about multiple sclerosis. Furthermore, a specific tool for evaluating multiple sclerosis information was developed, contributing to the debate about suitable criteria for measuring the `quality' of health information on the web.