Non-adherence to insulin treatment is common in adolescents and young adults (AYAs) with type 1 diabetes (T1D) and is associated with increased morbidity and mortality. However, the socio-cognitive determinants (SCDs) of adherence in AYAs with T1D are less frequently represented in systematic reviews. This systematic review aimed to investigate the key SCDs associated with adherence/non-adherence to insulin treatment in AYAs in the age range of 17-24 years with T1D. A systematic review in PubMed, Embase, Web of Science, and PsycINFO was conducted. The search took place from 2021, to January 1st, 2022, and was repeated on June 5-7, 2022 and from July 18 to July 24, 2023. The methodological quality of studies was assessed by the National Heart, Lung, and Blood Institute quality assessment tool for observational cohort and cross-sectional studies. Six articles representing 973 AYAs with T1D were included for data extraction. The identified SCDs included risk perceptions, attitude, family and friends' social support, self-efficacy, and information factors. However, there was inconsistency in correlational findings among studies. The identified SCDs influencing insulin adherence in AYAs with T1D could serve as targets for patients' consultations and tailored interventions to improve adherence and overall health outcomes, as well as for policymakers to integrate these interventions into diabetes care planning. However, further research in the area of factors affecting insulin adherence in quality-designed studies that use detailed and comprehensive measures for assessing adherence is needed.