OBJECTIVE: Estimating glycemic variability (GV) through within-day coefficient of variation (%CVw) is recommended for patients with type 1 Diabetes (T1D). High GV (hGV) is defined as %CVw > 36%. However, continuous glucose monitoring (CGM) devices provide exclusively total CV (%CVT). We aimed to assess consequences of this disparity. RESEARCH DESIGN AND METHODS: We retrospectively calculated both %CVT and %CVw of consecutive T1D patients from their CGM raw data during 14 days. Patients with hGV with %CVT >36% and %CVw ≤36% were called the "inconsistent GV group". RESULTS: A total of 104 patients were included. Mean ± SD %CVT and %CVw were 42.4 ± 8% and 37.0 ± 7.4% respectively (P < 0.0001). Using %CVT, 81 patients (73.6%) were classified as having hGV, whereas 59 (53.6%) using %CVw (P < 0.0001) corresponding to 22 patients (21%) in the inconsistent GV population. CONCLUSIONS: Evaluation of GV through %CV in patients with T1D is highly dependent on the calculation method and then must be standardized.