Amyotrophic lateral sclerosis is the most common motor neuron disorder in 
adults. Although the diagnosis appears obvious in theory, clinical practice 
shows the contrary as diagnosis is delayed in many patients; the average time 
between symptom onset and diagnosis can reach 12 months. The delay can be 
explained by the variability of the clinical presentation and by the absence of 
diagnostic markers. In order to standardize diagnosis for enrollment in clinical 
research, diagnostic criteria for ALS were created and revisited during the last 
20 years. In 2006, the Awaji criteria for the diagnosis of ALS were proposed, 
adding two major points to the diagnostic criteria: electromyography is 
considered equivalent to clinical examination for the identification of LMN 
signs and fasciculation potentials resume their prominent place in the 
diagnosis. Comparisons of the accuracy of the revisited El Escorial and Awaji 
criteria support improved diagnostic sensitivity without any effect on 
specificity with the new classification. The only weakness of the new 
classification involves patients with UMN signs in one region and LMN in two 
regions; these patients were previously classified as laboratory-supported 
probable ALS and currently as possible ALS, a lower level of diagnostic 
certainty. In all other instances the accuracy appears to be improved by the 
Awaji criteria. Nevertheless, there is a body of evidence suggesting the need 
for a revision of these new criteria, giving more weight to clinical and 
complementary findings of UMN involvement. The need to diagnose and treat ALS 
quickly could be facilitated by the inclusion of complementary investigations 
that detect UMN signs.