The aim of the present study was to analyse the survival rate in a group of breast cancers detected in the intervals between screening examinations in relation to clinically detected cancers in a non-screened population. All interval and control cancers were recruited from a randomized controlled mammography screening trial in Stockholm. The overall survival up to eight years of observation was higher in 191 patients with interval cancers than in 142 control cancers (p = 0.01). There were no significant differences between the two groups with regard to tumor size, stage distribution, or mean age, though the interval group did have a larger proportion of younger women. The similarity was confirmed by multiple regression analysis. The overall survival stage by stage was consistently higher in interval cancers. The survival rate in the true interval cancers was similar to that for those found in retrospect to have been detectable or traceable at the time of screening. No correlation was found between the length of the interval and the survival of patients with interval cancers. These results contradict the hypothesis that a high growth rate is associated with a poorer prognosis and that interval cancers are a more aggressive form of breast neoplasia.