Interval cancer is cancer detected between screening rounds among screening participants. In the Norwegian Breast Cancer Screening Programme, 19 per 10,000 screened women are diagnosed with interval cancer. We conducted semi-structured interviews with 26 such women. The women interpreted their interval breast cancer in two ways: that mammography can never be completely certain, or as an experience characterized by shock and doubts about the technology and the conduct of the medical experts. Being diagnosed with interval cancer thus influenced their trust in mammography, but not necessarily to the point of creating distrust. The women saw themselves as exceptions in an otherwise beneficial screening programme. Convinced that statistics had shown benefits from mammography screening and knowing others whose malignant tumours had been detected in the programme, the women bracketed their own experiences and continued trusting mammography screening. Facing a potentially lethal disease and a lack of alternatives to mammography screening left the women with few options but to trust the programme in order to maintain hope. In other words, trust may not only be a basis for hope, but also a consequence of it.