AIM: Amyotrophic lateral sclerosis (ALS) is a progressive disease characterized by degeneration in the upper and lower motor neurons of the corticospinal tract, brain stem, and spinal cord. Recent studies have revealed that the disease does not present solely with motor neuron involvement. Accordingly, the aim of this study is to investigate the presence of cardiac autonomic impairment in patients diagnosed with ALS. MATERIAL AND METHOD: A total of 61 patients, who were diagnosed with ALS according to the Revised El Escorial Criteria (R-EEC), were included in this prospective study, in addition to the 29 healthy individuals, who were included in the study as controls. In order to assess the cardiac autonomic involvement, the presence of orthostatic hypotension was investigated, and transthoracic echocardiography and 24-hour electrocardiogram (ECG) using a Holter monitor were performed. RESULTS: Orthostatic hypotension was detected in 14 (22.2%) patients. Holter electrocardiogram results of the patient group revealed statistically significantly lower heart rate variability (HRV) indicators in the time domain (SDNN, SDANN, SDNN index, rMSSD, and pNN50) and in the frequency domain (high frequency [HF], low frequency [LF], and very low frequency [VLF]) than those of the control group (P < .05). CONCLUSION: Contrary to the popular opinion, cardiac autonomic dysfunction in patients with ALS can occur at any stage of the disease. Therefore, it is recommended that the patients are evaluated via periodic examinations during the follow-up period for cardiac autonomic involvement.