BACKGROUND AND AIM: Glycated hemoglobin (HbA1c) assessment is basic to diabetes management. Little is done to describe the whole spectrum of the trajectory, its related temporal patterns of metabolic indices, and comorbidities. METHODS AND RESULTS: This was a longitudinal study. In the Diabetes Management through Integrated Delivery System project in Taiwan, enrollees had diabetes, but no major comorbidities. They were randomized into intensive or conventional education (health, diet and exercise) groups. HbA1c was classified by a groupbased trajectory model on the basis of repeated six-monthly measurements. We analyzed data from 1091 subjects who had at least two measurements on HbA1c. HbA1c exhibited three distinct ranges of low (42-53 mmol/mol), intermediate (64-75 mmol/mol) and high (97 mmol/mol), all of which persisted for 4.5 years regardless of receiving intensive education or not. Temporal changes and a time-group interaction were found for triglycerides, total cholesterol, HDL-C and LDL-C. The high trajectory was associated with the major co-morbidities of retinopathy, nephropathy, neuropathy, stroke, hypoglycemia, and ketoacidosis. Patients in the intensive education group (62.4%), which were equally distributed in the three trajectories, had significantly lower HbA1cs (-0.14%= -1.5 mmol/mol, p=0.026). The intermediate trajectory patients with intensive education had HbA1cs higher than the low trajectory patients with conventional education (β=0.189, p=0.033). Though not significant, a similar pattern was found for DM education in the high group (β=0.223, p=0.154). CONCLUSIONS: Novel strategies beyond current education and pharmacotherapeutic regimens are needed to lower HbA1c at least 11 mmol/mol for the high HbA1c group to minimize comorbidities.