Coinciding with the relatively good and improving prognosis for patients with stage I–III breast cancer, late recurrences, new primary tumours and late side-effects of treatment may occur. We gained insight into prognosis for long-term breast cancer survivors. Data on all 205 827 females aged 15–89 diagnosed with stage I–III breast cancer during 1989–2008 were derived from the Netherlands Cancer Registry. Conditional 5-year relative survival was calculated for every subsequent year from diagnosis up to 15 years. For stage I, conditional 5-year relative survival remained ∼95% up to 15 years after diagnosis (a stable 5-year excess mortality rate of 5%). For stage II, excess mortality remained 10% for those aged 15–44 or 45–59 and 15% for those aged 60–74. For stage III, excess mortality decreased from 35% at diagnosis to 10% at 15 years for those aged 15–44 or 45–59, and from ∼40% to 30% for those aged ≥60. Patients with stage I or II breast cancer had a (very) good long-term prognosis, albeit exhibiting a small but significant excess mortality at least up to 15 years after diagnosis. Improvements albeit from a lower level were mainly seen for patients who had been diagnosed with stage III disease. Caregivers can use this information to better inform (especially disease-free) cancer survivors about their actual prognosis.