Chemotherapy for different types of cancer is often life-saving. On the other hand, the spectrum of side effects may involve the central nervous system (CNS) and lead to severe emotional and cognitive disturbances, a syndrome often referred to as “The Chemo Brain”. Here we report on a then 43-year-old female patient who first pre- sented to our clinic in 2013 and in whom breast cancer of the right breast had been diagnosed four years earlier. At that time she became a patient of the Comprehensive Cancer Center of the University of Ulm (CCCU) and underwent breast-conserving therapy starting with systemic che- motherapy according to the rules of the GeparQuinto Study. This was followed by breast-conserving operation including axillary lymphono- dectomy. Histological examination of the excised material revealed an invasive ductal mammary carcinoma the exact staging of which will be reported in detail. Convalescence of the patient was protracted, and she continued complaining of difficulties to concentrate and to remember what she had been told or read shortly before. In addition, she com- plained of frequent mood swings. Therefore, she was referred to our department. Exploring her case history, we learned that she had worked as a manager of a car rental company which she had no longer been able to do after her cancer treatment because of her cognitive deficits. Beside clinical and psychiatric examination, our diagnostic procedures included electroencephalography (EEG), magnetic resonance tomography (MRT) of the brain using gadolinium enhancement, and extensive neuropsycholo- gical testing. In detail, components of the Wechsler Adult Intelligence Scale (WAIS), the Ray Auditory Verbal Learning Test (RAVLT), the Multiple Choice Vocabulary (“Mehrfachwahl-Wortschatztest”), the “Regensburger Wortflüssigkeitstest” (Regensburg Word Fluency Test, RWT), and the “Testbatterie zur Aufmerksamkeitsprüfung” (Test Battery for the Assess- ment of Attention, TAP) were applied. Whereas the EEG was unremarkable, the MRT performed in 2013 showed brain atrophy with frontotemporal accentuation. As an accessory finding, an arachnoid cyst was detected at the left temporal pole. No metastases were found. Interestingly, we had the opportunity to compare these findings with those of an earlier MRT performed in 2011. In the latter one, the arachnoid cyst was also visible, but there was no pronounced brain atrophy. These observations raise the question if progressive brain atrophy might be associated with the syndrome of “Chemo Brain”. Neuropsychological examination revealed severe cognitive deficits in this patient – details of which will be reported – apparently due to the chemotherapy she had undergone. Possible mechanisms of action, treatment options, and ethical implications will be discussed.