OBJECTIVES: The number of patients seeking cancer information over the internet is increasing. However, it is unknown what kind of information sources is available online in Japan, UK and USA. The objective of the study is to evaluate the information sources related to breast cancer and to compare the information source among Japan, UK and USA. METHODS: We identified top-rated 20 information sites and the number of advertisements on the initial screen by using a key word as “Breast cancer” on Yahoo and Google sites in Japan, UK and USA. Information sources were defined and categorized into six kinds of information organizers; public institutes, academic associations, NGO/NPOs, information portal, advertisements, and corporate sponsored sites. The each information source was categorized by two evaluators independently. Third evaluator reconciled and decided the category of the information source if evaluation results were not identical between two evaluators. The proportion of internet sources by six categories was calculated and compared among three countries. RESULTS: In Japan, the proportion of information sources by public institutions and academic associations was 30%. Less than 10% of information sources were by NGO/NPOs. More than half of information sources were advertisements. In UK, 70% of information sources were provided by NGO/NPOs whereas less than 20% of information sources were advertisement. In USA, 30% of information sources were by academic institutions whereas more than 50% of information sources were by information portal. CONCLUSIONS: This comparative survey provides an overview of information sources related to breast cancer available on the internet. The number of top-rated information sites by public institutes, academic associations was low compared to UK and USA. There were a few information sources by NGO/NPO in Japan.