Method: In Scania (Skåne), the most southern county in Sweden, 84,039 infants were born during the period 1999–2005. By the end of April 2013, 324 of those children had been diagnosed with T1D. For each of those T1D children three control children were randomly selected and matched for HLA genotype and birth year. Individually modelled exposure data at residence during pregnancy were assessed for nitrogen oxides [NOx], traffic density and ozone.