Cognitive impairment, especially verbal episodic memory and executive function impairments, has been considered to be a possible adverse effect of aromatase inhibitors (AI). This phase III open-label study compared the impact of tamoxifen and AI on verbal episodic memory (Rey auditory verbal learning test-RAVLT) and other cognitive functions (visual memory, psychomotor speed, and executive functions) after 6 and 12 months of treatment in breast cancer patients undergoing adjuvant hormonotherapy. Menopausal chemo-naïve patients with resectable breast cancer were randomly assigned (1:1) at the end of the radiotherapy to receive tamoxifen or AI. Neuropsychological assessments, self-reported quality of life, and depression assessments were performed at baseline, before any hormonal treatment, and at 6 and 12 months. Mixed design analysis models of variance was used to compare the evolution of the scores between the groups during follow-up. A total of 74 evaluable patients were enrolled (Tamoxifen arm, n = 37; AI arm, n = 37; letrozole n = 18; anastrozole n = 16; exemestane n = 3). The median age at inclusion was 61 years (range, minimum 49-maximum 69). The patient and breast cancer characteristics were well balanced between arms. After 6 months, no significant differential effect of AI or tamoxifen was observed on the RAVLT. Moreover, considering the other cognitive measures and the quality of life questionnaires, there were also no differences between the groups during the 1-year follow-up. In this study, AI has not demonstrated worse adverse effects on cognitive functions than tamoxifen during a 1-year follow-up.