For patients with type 1 diabetes, sense of coherence (SOC), locus of control (LOC) and depression symptoms seem to be important variables in the context of compliance with a treatment regimen. The aim of this article is to describe the functioning of adolescents with type 1 diabetes—to define the common features and differentiating characteristics of the clinical group in comparison with the control group in terms of SOC, LOC and symptoms of depression. The other aim is to check whether LOC mediates the relationship between SOC and depression symptoms in the diabetics group. The study involved 100 adolescents aged 13–17. The clinical group contained adolescents with type 1 diabetes while the control group featured adolescents without diabetes. Antonovsky’s Sense of Coherence Scale (SOC-29), the Locus of Control Questionnaire (LOCQ) by Krasowicz and Kurzyp-Wojnarska and the Children’s Depression Inventory (CDI) by Kovacs were used. The groups did not differ in their SOC level but varied in the level of depression symptoms and LOC. The clinical and control groups had undetermined and external LOC, respectively. Diabetics also had a lower level of depression symptoms. SOC correlated positively with LOC and negatively with depression symptoms. Additionally, within the clinical group, LOC mediated the relationship between SOC and symptoms of depression. Determining the level of key health variables in type 1 diabetics is important in educating them how to manage their disease. With regard to adolescents without diabetes, the results confirm the need to intensify activities aimed at monitoring their mental state.