OBJECTIVES:  To validate self-reported patient survey data on diabetes self-management using patient’s electronic medical records (EMR). METHODS:  The cross-sectional study included patients (age≥18 years) diagnosed with type 2 diabetes mellitus (T2DM) (ICD-9 code: 250.xx) and had ≥2 physician visits. The sample was identified from a physician group’s EMR database. A mail-based survey assessing diabetes self-management practices was administered to a random sample of 2,100 patients, stratified into three groups based on HbA1c level: <7, 7-9, and >9. Patient survey responses were then linked to their EMR data using unique patient codes. A ‘concurrent triangulation design’ was then employed to validate and substantiate patient survey responses with the EMR database for variables that were common in the two databases such as demographics, comorbidities, HbA1c, year since diagnosis, and diabetes medications. Descriptive, comparative and correlational analyses were conducted using IBM SPSS Statistics 24.0. RESULTS:  A total of 210 responses were received (10% response rate). Self-reported age (mean: 63.7±11.7 years) and age from EMR (mean: 64.5±12.2 years) were strongly correlated (r=0.94, p<0.001). Marital status (ρ=0.72, p<0.001), race (ρ=0.69, p<0.001), and gender (ρ=0.99, p<0.001) showed strong significant correlation as well. Moderate correlation (r=0.63, p<0.001) was observed between self-reported HbA1c (mean: 7.8±1.7) and HbA1c from EMR (mean: 7.9±1.7). Additionally, important clinical variable such as HbA1c in the EMR data had fewer missing values (n=7) compared to self-report data (n= 59). CONCLUSIONS: Since the patient groups were based on HbA1c, it was an extremely important variable and yet, HbA1c data was missing for 28.1% of survey respondents. Supplementing EMR data not only validated the survey responses, but also enabled substitution of survey reported HbA1c with HbA1c from EMR. The use of mixed-method research offers an in-depth understanding of the data and overcomes the limitations of a single method.