To develop two evaluation tools for weight loss and weight gain advertisements on the Internet in order to help consumers to evaluate the quality of information within these advertisements. One hundred websites identified by Internet search engines for weight loss and weight gain strategies (50 websites each) were evaluated using two specific scoring instruments, developed by adapting questions from the 'DISCERN' tool and reviewing all related weight control guidelines and advertising regulations. The validity and reliability of the adapted tools were tested. Our evaluation tools rated the information from most websites as poor quality (70%). In the case of weight loss strategies, statements about rapid (18%) and permanent (28%) weight loss caused concern as well as lack of sensible advice about dieting and a lack of product warnings (84%). Safety concerns relating to weight gain products were the lack of warnings about side effects in products containing steroids and creatine (92%). The adapted tools exhibited acceptable validity and reliability. Quality of information within weight control advertisements on the Internet was generally poor. Problems of false claims, little advice on healthy ways to modify weight and few warnings on side effects have been highlighted in this study.