This thesis aimed to investigate three related research questions: (1) is the quality of life (QoL) for adolescents with Type 1 Diabetes (T1D) and parents of children with T1D positively related to their levels of self-efficacy; (2) is the relationship between self-efficacy and QoL for these adolescents and parents moderated by the severity of either their own or their child’s T1D, respectively, and; (3) how reliable is the use of parent proxy reporting in place of child self-report for a QoL measure. It was predicted that adolescents and parents with higher levels of self-efficacy would have higher levels of QoL. It was also predicted that the relationship between adolescents’ and parents’ levels of self-efficacy and QoL would be attenuated when their own or their child’s HbA1c values were high and strengthened when their own or their child’s HbA1c values were low, respectively. As the third aim of this thesis was exploratory in nature no predictions were made. To answer the above questions, twenty-four adolescents with T1D and 104 parents of children with T1D completed one of two questionnaires assessing their diabetes self-efficacy, their QoL, and in the case of parents, their child’s QoL as well. As predicted, the findings revealed that adolescents and parents with higher levels of self-efficacy reported experiencing better QoL. Contrary to hypotheses, however, T1D severity (as measured by HbA1c) did not moderate the positive relationship between self-efficacy and QoL for either adolescents or parents. Lastly, results of a paired samples t-test revealed no difference between parent’s proxy reports and their child’s self-reported QoL, thus providing support for the reliability of parent proxy reports in place of child self-reports. Explanations for these findings are discussed along with the theoretical and practical implications of the research. Potential avenues for extending upon the current research are also provided.