INTRODUCTION Japan is a developed country with high use of Internet and online platforms for health information. 'Yahoo! Answer Japan' is the most commonly used question-and-answer service in Japan. AIM To explore the information users seek regarding breast cancer from the 'Yahoo! Answer Japan' web portal. METHODS The 'Yahoo! Answer Japan' portal was searched for the key word 'breast cancer' and all questions searched for the period of 1 January to 31 December 2014 were obtained. The selected questions related to human breast cancer and were not advertisements or promotional material. The questions were categorized using a coding schema. High and low access of the questions were defined by the number of view-counts. RESULTS Among the 2392 selected questions, six major categories were identified; (1) suspected breast cancer, (2) breast cancer screening, (3) treatment of breast cancer, (4) life with breast cancer, (5) prevention of breast cancer and (6) others. The highest number of questions were treatment related (28.8%) followed by suspected breast cancer-related questions (23.4%) and screening-related questions (20%). Statistical analysis revealed that the treatment-related questions were more likely to be highly accessed. CONCLUSION Content analysis of Internet question-answer communities is important, as questions posted on these sites would serve as a rich source of direct reflection regarding the health-related information needs of the general population.