Background and aims Adolescents tend to have risky behaviours like aggression and self-injury due to the age period charateristics. The risk of aggression and self-injury may increase in adolescents with the addition of chronic diseases. This study was conducted descriptively to determine and compare the aggression and self- injury in those with type 1 diabetes mellitus (T1DM) and healhty adolescents.

Methods The study sample consisted of 60 adolescents with T1DM followed up in the child endocrinology polyclinic of a university hospital and 319 healthy adolescents,15–18 aged, at 9th^-12th grade at high school. In the study, the permission of the institution, Ethical Committee, the parent and adolescent consent, the data were collected using a questionnaire form, Agression Questionnaire (AQ) and Inventory of Statements About Self-injury (ISAS). The descriptive statistics, Shapiro-Wilk, Mann-Whitney U, student t, Ki-kare, Spearman correlation tests were used for analysing data.

Results The mean scores of AQ all subscales and the total scale of healthy adolescents were higher than adolescents with T1DM (p < 0.05). Mean ISAS scores of adolescents with T1DM were higher than the healthy adolescents (p > 0.05). The mean scores of autonomic function, social function and ISAS were positively moderately correlated with the mean scores of total aggression in both healthy and diabetic adolescents (p < 0.05).

Conclusions Considering the age period characteristics, giving weight to sport (especially team sports), social and cultural activities and education about anger-stress management and effective communication skill to adolescents and their families in school may be recommended.