Objectives Women with breast cancer share their experiences and emotions about the illness on Instagram – a tool understudied when it comes to chronic illness. The paper characterizes the women's activities, and both online self-disclosure and social sharing of emotions concepts are used to help explain the women's practices. Methods Using qualitative conventional content analysis, four profiles of women are manually analysed, with posts as the unit of analysis ( n = 811). Based on eleven subcategories, three broad analytical categories are introduced: self-disclosure of negative information (C1), self-disclosure of positive information (C2) and disclosure of information about other people (C3). Results The women post narratives about suffering resulting from cancer, and the fears they experience. Also, the posts relate to positive emotions, joyful life events, self-acceptance, or self-affirmation. While writing, the women share information about people supporting them on their way to recovery. Discussion The activity of women cannot be explained only by their online self-disclosure, where anonymity and lack of offline support are often emphasized. Women on Instagram are not anonymous and report on support by relatives and other people. Rimé's concept of social sharing of emotions is used to explain this phenomenon.