Objectives: (1) Adapt the ECAS into Greek, validate it in ALS patients and compare with the ALS-CBS. (2) Determine the sensitivity and specificity of ECAS in the differentiation between AD and non-demented ALS patients as compared with the ACE-III and mini-ACE. Methods: ALS patients (n = 28) were recruited and AD patients (n = 26) were matched in age, sex, and education with ALS patients (n = 24). The normative data were derived from a random sample of controls (n = 52). Bayes correlation analysis was conducted to examine convergent validity. Bayes t-test was performed to assess between groups’ differences. Receiver operating characteristics (ROC) curve analyses and area under the curve (AUC) were implemented to appraise the sensitivity and specificity in the differentiation between the AD and non-demented ALS patients. Results: The ECAS and its sub-scores in addition to the behavior interview demonstrated robust correlations with the ALS-CBS. Impairment in language and verbal fluency were the most prominent deficits in the ALS patients. The most frequently reported change was apathy. The ROC analysis demonstrated that the ECAS-ALS nonspecific score (comprising memory and visuospatial domains) is the most sensitive and specific in differentiating the AD from ALS patients. The other measures expressed high sensitivity, yet a poor specificity. Conclusions: The ECAS is a multi-purpose screening tool. The ECAS-ALS specific appraises the whole spectrum of the highly prevalent cognitive impairments in ALS. The ECAS-ALS nonspecific (memory and visuospatial) is a sensitive score to detect AD related deficits and is able to differentiate the AD from the non-demented ALS patients better than the ACE-III and mini-ACE.