Botulinum toxin type A (BoNT/A) has been proposed as an alternative treatment for sialorrhoea in patients with amyotrophic lateral sclerosis (ALS). In an open-label prospective study, BoNT/A was injected into the parotid glands bilaterally using anatomic landmarks in 26 ALS patients with bulbar symptoms. Two weeks after injection the severity of sialorrhoea and the related disability were evaluated subjectively and objectively. A group of healthy subjects acted as controls for saliva production. Patients also underwent electrophysiological tests to evaluate possible toxin effects in the nearby non-injected muscles by comparing the amplitude of compound motor action potentials (cMAPs) elicited by electrical stimulation and recorded from the orbicularis oculi and masseter muscles. After BoNT/A injections, of the 26 patients treated, 23 reported that the severity of sialorrhoea improved and the disabling symptoms diminished. Cotton roll weight also decreased after BoNT/A injection, suggesting a reduction in saliva production. Two patients complained of dry mouth. BoNT/A injection left the cMAP amplitude unchanged, suggesting that botulinum toxin does not significantly affect the non-injected facial and masticatory muscles. In conclusion, intraparotid anatomically-guided BoNT/A injection is an effective, easy, and safe treatment for sialorrhoea in patients with bulbar symptoms related to ALS.