This study looks at how a mobile based app called 'Dose Check' used along with Tresiba helps to control blood sugar level in participants with type 2 diabetes mellitus. Participants will get Tresiba as prescribed by the study doctor or participants will continue already prescribed treatment with Tresiba. Participants will also be prescribed to use Dose Check app by the study doctor and will be asked to install the Dose Check app in their mobile phone, which will support participants with the correct dose of Tresiba. This study will last for about 6 to 7 months.

Inclusion Criteria:

• Signed consent obtained before any study-related activities (study-related activities are any procedure related to recording of data according to the protocol).
• Male or female, age above or equal to 21 years at the time of signing informed consent.
• Diagnosed with type 2 diabetes mellitus (T2DM) above or equal to 12 weeks prior to signing consent.
• The decision to initiate treatment with commercially available Dose Check app as a part of treatment along with Tresiba as per the local label, has been made by the participant and the treating physician before and independently from the decision to include the participant in this study.
• Available HbA1c value less than or equal to 12 weeks prior to the 'Informed consent and initiation of Dose Check app visit' (V1) or HbA1c measurement taken in relation with the 'Informed consent and initiation of Dose Check app visit (V1)' (V1) or planned soon after V1 (less than or equal to 7 days), if in line with local clinical practice.
• Willingness to continue using the Dose Check app on a compatible smartphone according to the intended use for the entire duration of the study.

Exclusion Criteria:

• Previous participation in this study. Participation is defined as having signed informed consent in this study.
• Women known to be pregnant or breastfeeding, or women planning to become pregnant during the conduct of the study.
• Treatment with any investigational drug or software as medical device (SaMD) within 30 days prior to enrolment into the study.
• Diagnosed with type 1 diabetes mellitus.
• Mental incapacity, unwillingness or language barriers precluding adequate understanding or cooperation.
• Hypersensitivity to the active substance or any of the excipients as specified in the Tresiba local label.
• On treatment with Tresiba for above 3 months or at dose above 20 units at Informed consent and initiation of Dose Check app visit (V1).

Participants with T2DM and aged less than or equal to 21 years.

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