BACKGROUND Autonomic dysfunction (AD) is a common and important complication in Guillain-Barré syndrome (GBS) and may be the cause of significant morbidity or death. Limited studies have evaluated this complication in childhood GBS. Our objectives were to show the prevalence of AD in children with GBS and investigate its association with the severity of the disease. METHODS Study included 28 children admitted with a diagnosis of GBS. Heart rate variability (HRV), motor function disability of the upper limbs and GBS disability scores were measured at admission and the results were compared with 20 healthy age/gender matched subjects (2-13 years; 43% male). GBS subtypes were defined by electromyography: acute inflammatory demyelinating polyneuropathy (AIDP) or acute motor axonal neuropathy (AMAN). RESULTS The mean age was 5.5±3.4 years (range 1.5-14 years; 50% male). AIDP and AMAN subtypes comprised 57.1% and 42.9% of cases, respectively. In the upper limbs, 85.7% and in the GBS disability grading, 50% of patients had ≤ 3 scores, implying less severe motor dysfunction. There was no difference in the mean heart rate between patients vs. controls (103.9 vs. 98.2 bpm; P= 0.16), but half of patients showed AD and HRV was significantly reduced in patients compared to controls. Of the 16 patients with AIDP, 11 (68.8%) showed reduced HRV compared to 3 (25%) out of 12 AMAN cases (P= 0.02). There was no significant relation between HRV and motor disability scores. CONCLUSIONS AD was present in half of children with mild GBS and it showed no significant association with disease severity.