The study will look at how well insulin icodec controls blood sugar levels in participants who have never used it before. Participants with type 1 diabetes (T1D) will be treated with insulin icodec as prescribed to by their doctor, in accordance with usual clinical practice. This study will last for about 22 to 30 weeks.

Inclusion Criteria:

• Signed consent obtained before any study-related activities (study-related activities are any procedures related to recording of data according to the protocol).
• The decision to initiate treatment with commercially available insulin icodec has been made by the participant/legally acceptable representative (LAR) and the treating physician before and independently from the decision to include the participant in this study.
• Male or female, age greater than or equal to (≥) 18 years at the time of signing informed consent.
• Diagnosed with T1D ≥ 1 year before signing informed consent.
• Treated with multiple daily insulin injections (daily basal insulin analogue and bolus insulin analogue regimen) ≥ 6 months before signing informed consent.
• Available HbA1c value less than or equal to (≤) 90 days prior to the 'Initiation visit' (V1) or HbA1c measurement taken in relation with the 'Initiation visit' (V1) if in line with local clinical practice.
• Treatment naïve to once-weekly insulin prior to the 'Initiation Visit' (V1).

Exclusion Criteria:

• Previous participation in this study. Participation is defined as having given informed consent in this study.
• Treatment with any investigational drug within 30 days prior to enrolment into the study.
• Mental incapacity, unwillingness or language barriers precluding adequate understanding or cooperation.

The study population comprises participants who are diagnosed with type 1 diabetes and agree to be treated with insulin icodec after consultation with their physician independently from the decision to participate in this study.

According to the Novo Nordisk disclosure commitment on novonordisk-trials.com