Sporadic amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder affecting upper and lower motoneurons. There is an approximately 2:1 higher incidence of ALS in men compared to women, and this has raised the hypothesis of an involvement of sex hormones in the etiopathogenesis of the disorder. In this work, the serum levels of dehydroepiandrosterone sulphate (DHEAS), 17-betaestradiol, free and total testosterone were measured in 35 patients with defined or probable ALS, according to the El-Escorial/WFN revisited criteria, and compared to those obtained from 57 disease controls, matched for age and gender to the ALS group. We found no differences between ALS cases and disease controls in the serum levels of DHEAS, 17-betaestradiol and total testosterone. Conversely, free testosterone was significantly decreased in the ALS group. Given that testosterone crosses the blood-brain barrier only as unbound form, we suggest a possible involvement of this sex hormone in the pathophysiology of this severe motor neuron disease.