The aim of the study was to check the prevalence of unipolarity (depression), bipolarity, as well as the quality of sleep and temperament traits in patients with type 1 diabetes (T1DM) who are provided with optimal conditions of diabetes care and to identify possible risk factors connected with affective traits. Out of the 107 T1DM patients, 78 (54 females, 24 males) were included for the analysis (HbA1c [%] 7.11±1.0, BMI [kg/m2 ] 25.3±5.6; Years of disease duration [N] 13.7±8.3). The patients filled in a set of questionnaires during their regular visit to the outpatient clinic. Three patients from the whole group were on intensive insulin therapy with Multiple Daily Injections (MDI) and Self-Monitoring of Blood Glucose (SMBG), all the rest were on various types of personal insulin pumps (years on insulin pump [N] 9.1±4.5). All the patients were on regular diabetologist care, with regular visits in a Centre for Advanced Technologies in Diabetes (at least every 6months). In QIDS-S (full explanation and abbreviation26 patients (33.8%) were screened positive for depression, in PHQ (full explanation and ab 57.7% of the patients (45 patients) had symptoms of depression (age was negatively correlated with PHQ score [r=-0.26; p=0.023]). In CES-D 16 (20%) of the patients assessed their present affect as depressed. None of the analysed clinical variables correlated with depression scores. In the Mood Disorder Questionnaire (MDQ), 16 patients reported having symptoms of bipolarity (20.5% vs. 79.5%). Hypomania Checklist (HCL) analysis indicated 10 patients with bipolar traits (>14) (14.9% vs. 85.1%). None of the analysed clinical variables correlated with HCL results. 11.5% of patients were indicated to be of morning type. Morningness was more often seen in younger patients (r=0.39; p=0.001). As many as 46.6% declared that they had poor sleep quality. The temperament traits analysis correlated with clinical parameters: Cyclothymic temperament trait was negatively correlated with age (r=-0.30; p=0.007) and positively with HbA1c level (r=0.30; p=0.025). Hyperthymic temperament was positively correlated with (BMI r=0.28; p=0.016). Quality of sleep was highly correlated with depressive symptoms CESD (r=0.61, p=0.001), PHQ Score (r=0.62; p=0.001), QISD (r=0.68; p=0.001) and bipolarity MDQ (p=0.50, p=0.001) and HCL (r=0.42, p=0.001). In addition, QIDS was shown to be correlated with the following features of temperament: depressive factor (r=0.41; p=0.001), irritable factor (r=0.53; p=0.001), cyclothymic factor (r=0.59; p=0.001), anxious factor (r=0.58, p=0.001). The prevalence of affective disorders and poor sleep quality in the examined T1DM patients was much higher than in the general population. Even if the patients have in general good glycaemic control, their mental health condition should not be neglected. Well organised cooperation between patients, diabetologists, psychiatrists and psychotherapists is needed (Clinical Trials Identifier: NCT04616391).