Cohort studies have indicated that avoidance of neuromuscular blocking agents (NMBA) is a risk factor for difficult tracheal intubation. However, the impact of avoiding NMBA on tracheal intubation, possible adverse effects, and postoperative discomfort has not been evaluated in a systematic review of randomised trials. We searched several databases for trials published until January 2017. We included randomised controlled trials comparing the effect of avoiding vs using NMBA. Two independent authors assessed risk of bias and extracted data. The risk of random errors was assessed by trial sequential analysis (TSA). We included 34 trials (3565 participants). In the four trials judged to have low risk of bias, there was an increased risk of difficult tracheal intubation with no use of NMBA [random-effects model, risk ratio (RR) 13.27, 95% confidence interval (CI) 8.19–21.49, P<0.00001, TSA-adjusted CI 1.85–95.04]. The result was confirmed when including all trials, (RR 5.00, 95% CI 3.49–7.15, P<0.00001, TSA-adjusted CI 1.20–20.77). There was a significant risk of upper airway discomfort or injury by avoiding NMBA (RR=1.37, 95% CI 1.09–1.74, P=0.008, TSA-adjusted CI 1.00–1.86). None of the trials reported mortality. Avoiding NMBA was significantly associated with difficult laryngoscopy, (RR 2.54, 95% CI 1.53–4.21, P=0.0003, TSA-adjusted CI 0.27–21.75). In a clinical context, one must balance arguments for using NMBA when performing tracheal intubation.