Amyotrophic lateral sclerosis is a progressive neurodegenerative disease resulting in loss of upper and lower motoneurons. Here we analyzed the clinical and epidemiological data of 202 ALS patients admitted to our department between 1950 and 2004. Risk and protective factors influencing onset and progression of the disease were examined. We also analyzed the relationship between first clinical symptoms/signs and prognosis of the disease. Our data suggest the importance of toxic factors in the initiation of the disease and the effect of clinical phenotype on the progression of ALS.