Background: The aim was to compare the accuracy of the Dexcom® G4 Platinum continuous glucose monitor (CGM) sensor inserted on the upper arm and the abdomen in adults. Methods: Fourteen adults with type 1 diabetes wore two CGMs, one placed on the upper arm and one placed on the abdomen. Three in-clinic visits of 5 h with YSI (2300 STAT, Yellow Springs Instrument) measurements as comparator were performed. Each visit was followed by 4 days with seven-point self-monitoring of blood glucose (SMBG) in free-living conditions. Accuracy analyses on the paired CGM-YSI and CGM-SMBG measurements of the two CGM sensors were performed. Results: Using YSI as comparator, the overall Mean Absolute Relative Difference (MARD) for the CGM_abd was 12.3% and CGM_arm was 12.0%. The percentage of the CGM measurements in zone A of Clarke error grid analysis for the CGM_abd was 85.6% and CGM_arm was 86.0%. The hypoglycemia sensitivity for the CGM_abd and CGM_arm was 69.3%. Using SMBG as comparator, the overall MARD for the CGM_abd was 12.5% and CGM_arm was 12.0%. The percentage of the CGM measurements in zone A for the CGM_abd was 84.1% and the CGM_arm was 85.0%. The hypoglycemia sensitivity for the CGM_abd was 60.0% and the CGM_arm was 71.1%. All the P-values from the comparisons between the accuracy of CGM_abd and CGM_arm were >0.05. Conclusion: The accuracy of a Dexcom G4 Platinum CGM sensor placed on the upper arm was not different from the accuracy of the sensor placed on the abdomen in adults with type 1 diabetes.