EDITOR—Updated results from the Malmö mammography screening trial have suggested that screening caused an over-diagnosis of breast cancer of 10% in women aged 55-69 years at randomisation.1 The authors noted that evidence from randomised trials on the level of overdiagnosis was lacking. This is not correct. On the basis of data from the Malmö trial,2 and the two trials from Canada,3 we have previously estimated a level of overdiagnosis of 30% (mean follow-up 8.8 years and 7 years, respectively)4 and have also suggested an over-diagnosis of 33% in …