Background and Aims: The risk of nocturnal hypoglycemia (NH) is a limiting factor for achieving good glycemic control in people with type 1 diabetes (T1D). Insulin degludec (IDeg) is proven to lower the risk of self-reported NH. As most episodes of NH are asymptomatic, we assessed differences in occurrence of NH by hourly plasma glucose (PG) measurements at treatments with IDeg or insulin glargine U100 (IGlar) in people with T1D suffering from recurrent nocturnal severe hypoglycemia. Materials and Methods: Pre-defined optional substudy of the HypoDeg trial, a 2-year investigator-initiated, randomized, cross-over trial where 149 participants with T1D were randomized to treatment with IDeg or IGlar. Fifty-one participants (mean (SD) age 58 (13) years, diabetes duration 28 (14) years and HbA1c 7.8 (1) %) were admitted for two nights for hourly blinded plasma glucose measurements for a minimum of one night (23:00h to 07:00h) during each 1-year treatment period. The primary endpoints were NH at level 1 (PG ≤ 3.9 mmol/L) and level 2 (PG < 3.0 mmol/L). Results: We collected data from 196 nights. A total of 57 nights (regardless of level) in 33 participants were hypoglycemic, including 20 nights with symptomatic hypoglycemia. The incidence of NH at level 1 was lower when treated with IDeg [17 events in 97 nights (18%)] as compared to IGlar [36 events in 99 nights (36%)], corresponding to a hazard ratio (HR) of 0.39 (95% CI: 0.22-0.71; p=0.002) during treatment with IDeg. At level 2, the incidence of NH was also lower during treatment with IDeg [8 events in 97 nights (8%)] as compared to IGlar [20 events in 99 nights (20%)], corresponding to an HR of 0.36 [95% CI: 0.16-0.80; p=0.013] during treatment with IDeg. Conclusion: In people with T1D and recurrent nocturnal severe hypoglycemia, treatment with IDeg as compared to IGlar results in a clinically significant lower rate of NH at both levels of hypoglycemia. Disclosure J. M. Brøsen: None. S. Lerche: None. K. Nørgaard: Advisory Panel; Self; Medtronic, Other Relationship; Self; Novo Nordisk Inc., Zealand Pharma A/S, Speaker’s Bureau; Self; Medtronic. H. D. Parving: None. L. Tarnow: None. B. Thorsteinsson: None. U. Pedersen-bjergaard: Advisory Panel; Self; Novo Nordisk A/S, Sanofi-Aventis, Consultant; Self; Abbott, Speaker’s Bureau; Self; Novo Nordisk A/S. R. Agesen: Employee; Self; Novo Nordisk. P. L. Kristensen: Speaker’s Bureau; Self; AstraZeneca, Eli Lilly and Company. A. Alibegovic: Employee; Self; Novo Nordisk A/S, Stock/Shareholder; Self; Novo Nordisk A/S. H. U. Andersen: Stock/Shareholder; Self; Novo Nordisk A/S. P. Gustenhoff: None. C. Hedetoft: None. T. Jensen: Stock/Shareholder; Self; Novo Nordisk A/S. C. B. Juhl: None. Funding Novo Nordisk