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Diabet. Med. 27, 1284-1288 (2010) Introduction There is some evidence of long-term tracking of HbA1c levels within diabetes centres, but little evidence of individual tracking. Methods HbA1c levels of children in the clinic over a period of 15 years were retrieved from the clinical chemistry laboratory information system. We measured the correlation of HbA1c between years (Spearman and Pearson rank correlation), as well as the relationship of HbA1c with age and the change over time in the clinic. Results Data were collected from 362 children and young people [158 female (44%)], aged 0-18 years (median 10.4 years), with 0-13.6 years of follow-up (median 4.7 years). Mean HbA1c levels fell from 9.3 ± 1.5% (78 ± 16 mmol/mol) in 2001 to 8.1 ± 1.3% (65 ± 14 mmol/mol) in 2009 in those at least 6 months after diagnosis ( P < 0.0001). HbA1c levels gradually rise with increasing age. HbA1c levels from year to year are significantly correlated. This is better for adjacent than subsequent years, but there is a significant correlation up to 9 years from diagnosis. Only 4 of 49 children with a 6-month HbA1c level of 9% (75 mmol/mol) or more had a long-term (2-5 years) median HbA1c < 8% (64 mmol/mol). Conclusions HbA1c levels track in individuals within an improvement in overall clinic levels, suggesting that, if optimal control can be achieved in the first 6 months, it can persist for up to 9 years. [ABSTRACT FROM AUTHOR]