DESCRIPTION (prepared by applicant): Intensive therapy for youths with type 1 diabetes mellitus (DM) yields higher HbA1c and more frequent severe hypoglycemia (SH) than for adults. The advent of continuous glucose sensors (CGS) could yield medical and psychological benefits for these youths. The investigators submit that many patients may not realize these benefits and that psychosocial features of patients and families will affect the outcomes of adding CGS to DM therapy. To maximize the therapeutic benefits of CGS, we need clinically useful information about its glycemic and psychological effects and about psychological influences on its therapeutic utility. This information would be useful in selecting candidates for this technology and for assisting patients and families in achieving positive outcomes from its use. This application addresses four specific aims: 1.) Evaluation of the effects of 12 month?s use of a CGS device (GlucoWatch Biographer, Cygnus, Inc.) on HbA1G, the Kovatchev Low Blood Glucose Index and the frequency of severe hypoglycemia; 2.) Identification of behavioral and psychological consequence of CGS use; 3.) Analysis of psychosocial predictors of metabolic and psychological outcomes; and 4.) Evaluation of glycemic profiles of healthy youths without DM, construction of a normative glycemic profile for use in future studies and comparison of the glycemic profiles of youths with and without diabetes. Specific Aims 1 through 3 will be addressed in a randomized, controlled trial of three intensive therapy regimens that are based on different glucose monitoring methods: SMBG patients will receive current intensive therapy with four to six self-monitored blood glucose tests daily; CGS with Feedback patients will augment SMBG by using a CGS device that gives immediate glucose feedback and alarms for high, low, and rapidly falling levels; CGS without Feedback patients will augment SMBG by using the same CGS device with the feedback and alarm functions disabled. Patients and parents will complete periodic assessments of demographic factors and general and diabetes-specific psychological factors. Statistical analyses will include multivariate analyses of variance, survival analysis and individual growth modeling techniques. Specific Aim 4 will be addressed by studying a demographically similar sample of 240 healthy children and adolescents who will use the GlucoWatch Biographer without feedback for a total of 144 hours during a two-week period. The project results will enhance clinical adoption of CGS technology.