Aims The risk of ischaemic heart disease (IHD) death in early type 1 diabetes onset was assessed using death certification data.

Methods The Yorkshire Register of type 1 Diabetes in Children and Young People was linked to clinically validated death certification data for those diagnosed under 15 years. Standardised mortality ratios (SMRs) were calculated using the England and Wales population and IHD death rates between 1978 and 2014 by 5-year age group and sex.

Results The cohort included 4382 individuals (83 097 person years). Of 156 deaths, nine were classed as IHD deaths before clinical validation. After clinical validation, 14 IHD deaths were classified, with an SMR of 13.8 (95% CI 8.2 to 23.3) and median age at death of 35.1 years (range 21.9–47.9 years).

Conclusions There is an early emergence of death from IHD in early onset type 1 diabetes. Underascertainment of IHD deaths was present without clinical validation of death certification.