Effectiveness and Safety Study of the DexCom™ G4 Continuous Glucose Monitoring System in Children and Adolescents With Type 1 Diabetes Mellitus

Inclusion Criteria: * 1\. Age 6 to \<18 years-old; * 2\. Have been diagnosed with type 1 diabetes mellitus and are on multiple daily injections (MDI) or Continuous Subcutaneous Insulin Infusion (CSII) insulin therapy; * 3\. Willing not to inject insulin or wear an insulin pump insertion set within 3 inches from the Sensor site during Sensor wear; * 4\. Willing to use only the blood glucose meter provided to them for self-monitoring of blood glucose (SMBG) during Sensor wear, and willing to adhere to the protocol-specified fingerstick schedule during home use; * 5\. Willing to participate in three consecutive 7-day Sensor wear periods; * 6\. Willing to take a minimum of 7 fingersticks per day during home use (2 for calibration purposes, 5 for comparative purposes); * 7\. Willing to refrain from the use of acetaminophen during the Sensor insertion period and for at least 24-hours prior to Sensor insertion; * 8\. Willing not to schedule an magnetic resonance (MRI) scan, computed tomography (CT) scan, or x-ray, for the duration of the study; * 9\. Both subject and guardian are able to speak, read, and write English. Exclusion Criteria: * 1\. Have extensive skin changes/diseases that preclude wearing the Sensor on normal skin (e.g. extensive psoriasis, recent burns or severe sunburn, extensive eczema, extensive scarring, extensive tattoos, dermatitis herpetiformis) at the proposed wear sites; 2. Subjects who have a known allergy to medical-grade adhesives; 3. For participants of childbearing potential: are pregnant as demonstrated by a positive pregnancy test within 72 hours of insertion (sexually active participants of childbearing potential must use birth control during this study); 4. Have a hematocrit that is less than 30%, or greater than 55%; 5. Current participation in another investigational study protocol (if a subject has recently completed participation in another drug study, the subject must have completed that study at least 30 days prior to being enrolled in this study); 6. Have any condition that, in the opinion of the Investigator, would interfere with their participation in the trial or pose an excessive risk to study staff (e.g., known history of hepatitis B or C).