Amyotrophic lateral sclerosis is an incurable neurodegenerative disease that is fatal with a median of 3-4 years. It is characterized by degeneration of the first and second motor neurons. In addition to physical limitations, neuropsychological abnormalities occur in more than 50% of cases. This leads to a rapid loss of autonomy and increases the need for care. An individual prognosis for the course of the disease, in particular the development of cognitive and behavioural abnormalities, is not yet possible As part of our investigations, we focused on cognitive performance and behavioural abnormalities measured by the Edinburgh Cognitive and Behavioural ALS Screen in patients with amyotrophic lateral sclerosis and investigated possible prognostic biomarkers in cerebrospinal fluid as well as modifiable factors such as nutrition and lung function. A retrospective data analysis of 99 patients with amyotrophic lateral sclerosis cases examined between 2018 and 2021 at the Department for Neurodegenerative Diseases and Gerontopsychiatry at the University Hospital of Bonn, using Edinburgh Cognitive and Behavioural ALS Screen, revealed that elevated levels of total tau and phospho-tau 181 were associated with diminished performance of patients with amyotrophic lateral sclerosis on the Edinburgh Cognitive and Behavioural ALS Screen. Additionally, weight loss during the course of the disease has been observed to have a deleterious impact on cognitive performance. Moreover, we were able to demonstrate a previously insufficiently described correlation between abnormalities in the Edinburgh Cognitive and Behavioural ALS Screen and low-normal thiamine levels in serum. The hypothesis that reduced lung function has a negative effect on cognitive performance was not supported by our findings. The initial onset of amyotrophic lateral sclerosis, whether bulbar or spinal, does not appear to affect cognition and behaviour measured using Edinburgh Cognitive and Behavioural ALS Screen. Furthermore, our findings confirm the utility of the Edinburgh Cognitive and Behavioural ALS Screen in identifying a behavioural variant frontotemporal dementia in amyotrophic lateral sclerosis patients who have been previously diagnosed by experienced neurologists using the Rascovsky criteria. This development facilitates a more precise utilization of complex diagnostic instruments. Our results provide insight into the prognosis of patients with amyotrophic lateral sclerosis in terms of cognitive performance and behavioural abnormalities as the disease progresses, as well as potential therapeutic approaches to stabilize and support neuropsychological abnormalities. The importance of total tau as a widely available prognostic marker should be emphasized. Additionally, new avenues of research are emerging, particularly regarding the role of thiamine in amyotrophic lateral sclerosis.