Non-communicable diseases, including diabetes, are partly responsible for the deceleration of improvements of life expectancy in many countries. Diabetes is also associated with sleep disturbances. Our aim was to determine whether sleep disturbances, particularly in people with diabetes, were associated with increased mortality risk. Data from the UK Biobank were analysed (n = 487,728, mean follow-up time = 8.9 years). The primary exposure was sleep disturbances, assessed through the question: Do you have trouble falling asleep at night or do you wake up in the middle of the night? The primary outcome was mortality. We also dichotomized sleep disturbances into “never/sometimes” versus “usually” (frequently), and combined with the presence/absence of diabetes: 24.2% of participants reported “never/rarely” experiencing sleep disturbances, 47.8% “sometimes” and 28.0% “usually”. In age- and sex-adjusted models, frequent sleep disturbances were associated with an increased risk of all-cause mortality (hazard ratio [HR], 1.31; 95% confidence interval [CI], 1.26–1.37), which remained significant in the fully adjusted model (HR 1.13, 95% CI 1.09–1.18). The presence of both diabetes and frequent sleep disturbances was associated with greater risk of all-cause mortality than either condition alone. In the fully adjusted model, the hazard ratio for all-cause mortality was 1.11 (95% CI, 1.07–1.15) for frequent sleep disturbances alone, 1.67 (95% CI, 1.57–1.76) for diabetes alone and 1.87 for both (95% CI, 1.75–2.01). Frequent sleep disturbances (experienced by more than one quarter of the sample) were associated with increased risk of all-cause mortality. Mortality risk was highest in those with both diabetes and frequent sleep disturbances. Complaints of difficulty falling or staying asleep merit attention by physicians.