Background: Type 1 diabetes mellitus (T1D) is a metabolic disease causing hyperglycemia due to β-cell destruction. Despite adequate treatment, complications such as diabetic retinopathy (DR) are common. The first aim was to investigate if acute onset of type 1 diabetes differed between those who had developed retinopathy and who had not after 15 years from diagnosis. The second aim was to investigate if mean glycosylated hemoglobin (HbA1c) levels affect the time to development of DR. Methods: The medical records of all children and adolescents diagnosed with type 1 diabetes during 1993–2001 in our area in Sweden were studied retrospectively and the mean HbA1c each year until the development of retinopathy was investigated. In total 72 patients were included and the follow-up time was between 15 and 23 years. Gender, p-glucose, age and HbA1c at diagnosis were analyzed for possible correlations to years to retinopathy. Results: HbA1c was significantly higher among those who had developed DR after 15 years from diagnosis, 98±9.2 (n=25) vs. 86±9.2 (n=46; p=0.025). A negative correlation was found between age at diagnosis and years to DR (rs=−0.376; p=0.026). Mean HbA1c levels at years 6–10 after diabetes diagnosis correlated significantly (rs=−0.354, p=0.037) to years until retinopathy. Mean HbA1c levels at years 1–15 after diabetes diagnosis were significantly higher at years 2–3 and years 5–8 for those who had developed retinopathy after 15 years from diagnosis. Conclusions: Higher HbA1c levels shortened the time to development of retinopathy. It is therefore important to keep HbA1c as close to normal as possible.