This trial was conducted in Europe. The aim of this study was to investigate the total exposure of NN5401 (insulin degludec/insulin aspart) in children, adolescents and adult subjects with type 1 diabetes.

Inclusion Criteria:

• Type 1 diabetes mellitus (as diagnosed clinically) for at least 12 months
• Body mass index for children: 15.0-20.0 kg/m^2 (both inclusive), for adolescents: 18.0-28.0 kg/m^2 (both inclusive) and for adults maximum 30.0 kg/m^2

Exclusion Criteria:

• Subject who has donated any blood or plasma in the past month, or more than 500 mL within 3 months prior to screening
• Not able or willing to refrain from smoking during the inpatient period
• Female of childbearing potential who is pregnant, breast-feeding or intends to become pregnant or is not using adequate contraceptive methods