Objective To determine the incidence of chronic comorbidities among children with type 1 diabetes (T1D) and to compare incidences with a group of children without diabetes.

Design Population-based cohort study.

Setting Dutch PHARMO database (1998–2010).

Patients All patients (<19 years old) with T1D between 1999 and 2009 (T1D cohort) and a group of age- and sex-matched (ratio: 1–4) children without diabetes (reference cohort).

Main outcome measure The incidence of nine common chronic comorbidities was assessed on the basis that they were treated pharmacologically and/or resulted in hospital admission. Cox proportional hazard analysis was used to estimate the strength of the association between T1D and comorbidities, expressed as HRs and 95% CIs.

Results A total of 915 patients with T1D and 3590 children in the reference cohort (51% boys, mean age of 10.1 (SD 4.5) years) were included. T1D was associated with an increased risk (HR; 95% CI) of hospitalisation for any comorbidity (3.7; 2.5 to 5.5), thyroid disease (14.2; 6.7 to 31.0), non-infectious enteritis and colitis (5.9; 3.0 to 11.5), cardiovascular disorders (3.1; 2.3 to 4.2), mental disorders (2.0; 1.4 to 3.1), epilepsy (2.0; 1.1 to 3.7) and (obstructive) pulmonary disease (1.5; 1.2 to 2.0). There was no significant difference in the incidences of other comorbidities (malignant disorders, anaemia and migraine) between the two cohorts.

Conclusions Our longitudinal study showed that incidences of six chronic diseases were significantly higher in T1D children during the early years of developing this disease compared with the reference children.