The fragility index represents the minimum number of patients required to convert an outcome from statistically significant to insignificant. This report assesses the fragility index of head and neck cancer randomised, controlled trials.

Studies were extracted from PubMed/Medline, Scopus, Embase and Cochrane databases.

Overall, 123 randomised, controlled trials were included. The sample size and fragility index medians (interquartile ranges) were 103 (56–213) and 2 (0–5), respectively. The fragility index exceeded the number of patients lost to follow up in 42.3 per cent (n = 52) of studies. A higher fragility index correlated with higher sample size (r = 0.514, p < 0.001), number of events (r = 0.449, p < 0.001) and statistical significance via p-value (r = −0.367, p < 0.001).

Head and neck cancer randomised, controlled trials demonstrated low fragility index values, in which statistically significant results could be nullified by altering the outcomes of just two patients, on average. Future head and neck oncology randomised, controlled trials should report the fragility index in order to provide insight into statistical robustness.