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Introduction Electrical stimulation of the upper airway dilator muscles is an emerging treatment for obstructive sleep apnea (OSA). Hypoglossal nerve stimulation (HNS) has recently been approved as treatment alternative to continuous positive airway pressure (CPAP) for selected patients with moderate to severe OSA, while transcutaneous electrical stimulation (TES) of the upper airway is being investigated as non-invasive alternative. Methods A systematic review and meta-analysis (CRD42017074674) including literature published up to May 2018 has been performed to investigate the impact of HNS and TES on OSA severity assessed by the apnoea-hypopnoea index (AHI) and the Epworth Sleepiness Scale (ESS) as measure of subjective sleepiness. Random-effects models were used. Heterogeneity and between study variance were assessed by I2 and τ2, respectively. The Robins-1 tool was utilised to assess the risk of bias for each study. Results Of the 41 clinical trials identified (n=1,853), data from 20 trials (n=895) could be pooled for meta-analysis (15 HNS [n=808], 5 TES [n=87]). Patient were predominantly middle aged (mean±SD 56.9±5.5years), overweight (body mass index, BMI 29.1±1.5kg/m2) with severe OSA (AHI 37.5±7.0h-1) and were followed-up for 6.9±4.0 month (HNS) and 0.2±0.4 months (TES), respectively. The AHI improved by -24.9 [95%CI -28.5, -21.2] h-1 in HNS (χ2 79%, I2 82%) and by -16.5 [95%CI -25.1, -7.8] h-1 in TES (χ2 7%, I2 43%; both p Discussion Both invasive and transcutaneous electrical stimulation reduce OSA severity by a clinically relevant margin. HNS results in a clinically relevant improvement of symptoms. However, data are mainly based on non-randomised trials.