Background: Cognitive impairment has been reported among breast cancer (BC) patients (pts) after adjuvant chemotherapy. However, very few studies focused on cognitive function at diagnosis. Here we aimed to describe cognitive impairment among recently diagnosed BC before any treatment. Methods: A predefined sub-study of the French national prospective cohort of cancer and toxicities performed extensive objective and subjective cognitive assessment before any BC treatment (surgery or neo-adjuvant treatment). This study included a group of pts with newly diagnosed invasive Stage I-III BC and a group of healthy control (HC) women matched on age and education level. Episodic and working memory, executive functions, processing speed, attention, cognitive complaints (FACT-COG), anxiety and depression (HADS) and fatigue dimensions (FA12) were assessed with neuropsychological tests and the referred self-report questionnaires. Objective and cognitive impairment were defined according to International Cognition and Cancer Task Force recommendations. Results: 264 women (median age 54±11 years) recently diagnosed (average of 37 days after initial diagnosis) with invasive BC (stage I-II, 69%) and 132 matched HC participated in this study. Impaired working memory (20% vs 4%), information processing speed (36% vs 17%), attention (16% vs 1%) and executive function (21% vs 8%) were higher among pts than in HC (p < 0.001). In addition, 24% (n = 64) of pts reported cognitive complaints versus 12% of HC (n = 16, p < 0.01). Emotional and cognitive fatigue were higher in pts than HC (mean 24 vs 15 and 18 vs 11, p < 0.01). Similarly, higher levels of anxiety and depression were observed in patients when compared with HC (respectively in 41% and 3% of patients vs 10 and 1% for HC, p < 0.001). Objective cognitive impairment was not associated with cognitive complains. Both objective and subjective cognitive impairment were not associated with anxiety or depression. However cognitive complain was associated with fatigue (p < 0.001). Conclusions: In this large study, compared to HC, patients recently diagnosed with a localized BC reported more cognitive complains and objective cognitive impairment before surgery, without link with emotional status, but with fatigue. Further understanding of the biology and correlates of cognitive dysfunction at BC diagnosis is needed (CANTO-NCT01993498).