Background and aims: higher glycaemic variability has previously been linked to an increased risk of hypoglycaemia. This post hoc analysis investigated the correlation between clinical within-day glycaemic variability, based on 9-point profiles, and hypoglycaemia in patients with type 1 (T1D) and type 2 diabetes (T2D). Materials and Methods: the correlation between within-day variability, based on 9 point profiles, and hypoglycaemia was investigated as a post hoc analysis in two double blind, treat-to-target, crossover trials comparing insulin degludec once daily (OD) with insulin glargine U100 OD in adults with T1D (SWITCH 1, n=501) or insulin-experienced adults with T2D (SWITCH 2, n=721). Within-day glycaemic variability was calculated as the relative fluctuation of the 9-point profile, defined through the integrated absolute distance from the mean. Variabilities were subsequently categorised into low, medium and high tertiles based on the geometric mean of the two 9-point profiles available per patient and treatment. Hypoglycaemia was defined as overall symptomatic (severe or blood glucose [<3.1 mmol/L (56 mg/dL)] confirmed), nocturnal symptomatic (00:01 05:59, both inclusive) and severe (requiring third-party assistance and confirmed by a blinded adjudication committee) events. Results: within-day variability was a significant predictor for the risk of overall and nocturnal hypoglycaemia in patients with T1D or T2D. However, no correlation was found for severe hypoglycaemia in this dataset. Conclusion: in conclusion, within-day glycaemic variability is associated with a risk of overall and nocturnal hypoglycaemia.