OBJECTIVES: Within the Dutch guidelines for treatment of Type 2 Diabetes Mellitus (T2DM), the target-value of HbA1c has been set at <7%. The aim of this study was to investigate the relationship between persistence with oral antidiabetic drug (OAD-)treatment and HbA1c goal-attainment in daily clinical practice. METHODS: From the PHARMO record linkage system, comprising among others, linked drug-dispensing, clinical laboratory, and hospital data for >2.3 million subjects in the Netherlands, new users of OADs were identified in the period 1999-2005. Patients who started on monotherapy with metformin, a sulphonylurea (SU), or a thiazolidinedione (TZD), or on combination therapy with metformin+SU, or metformin+TZD, with baseline HbA1c °Ý7% and at least one HbA1c-measurement in the period of 6-12 months after treatment-onset, were included in the study-cohort. Persistence with OAD-treatment in the first year of treatment was determined using the method of Catalan, and was defined as the duration of the first treatment-episode in days. In case the first treatment-episode overlapped with the date of a HbA1c-measurement, a patient was considered persistent at that measurement. Patients with HbA1c <7% were defined at goal. RESULTS: The study cohort included 2023 patients. Three-quarters (1512 patients) were persistent with any OAD at the time of first HbA1c-measurement in the time-period of 6-12 months after OAD-start: of these, 861 (57%) were at goal. Of the 511 patients who were non-persistent with any OAD at that time, 239 (47%) were at goal. Non-persistent patients were about 20% less likely to be at goal (RR-adj: 0.82; 95% CI: 0.74-0.91), compared to persistent users of any OAD. CONCLUSION: Non-persistent use of OADs leads to a 20% decreased chance of HbA1c goal-attainment in daily clinical practice. This effect of non-persistence seems modest, but represents a very large number of patients, in whom OAD-use might be better controlled.