Key Notes: Data from 8,020 children were analysed to identify associations between variations in type 1 diabetes and glycated haemoglobin (HbA1c) in Sweden. Girls had higher levels at diagnosis and follow up and many children with poor metabolic control still had high HbA1c several years later. A variation in month of onset was found, with 53% diagnosed during autumn and winter, but no seasonal variations in HbA1c were found during follow up.