Background Diabetes patients who fail to achieve early glycemic control may increase the future risk of complications and mortality. The aim of the study was to identify factors that predict treatment failure (TF) during the first year in adults with newly diagnosed type 2 diabetes mellitus (T2DM). Methods This retrospective cohort study conducted at a medical center in Taiwan enrolled 4,282 eligible patients with newly diagnosed T2DM between 2002 and 2017. Data were collected from electronic medical records. TF was defined as the HbA1c value 7% at the end of 1-year observation. A subgroup analysis of 2,392 patients with baseline HbA1c [greater than or equal to]8% was performed. Multivariable logistic regression analysis using backward elimination was applied to establish prediction models. Results Of all study participants, 1,439 (33.6%) were classified as TF during the first year. For every 1% increase in baseline HbA1c, the risk of TF was 1.17 (95% CI 1.15-1.20) times higher. Patients with baseline HbA1c [greater than or equal to]8% had a higher rate of TF than those with HbA1c Conclusions Newly diagnosed diabetes patients with baseline HbA1c [greater than or equal to]8% did have a much higher rate of TF during the first year. Subgroup analysis for them highlights the important predictors of TF, including medication adherence, performing SMBG, regular exercise, and gender, in achieving glycemic control.