Comparison of NN1250 With Insulin Glargine in Type 1 Diabetes

Inclusion Criteria: * Type 1 diabetes for 12 months or longer, hereof the last 3 months with injection based therapies * Current treatment with any basal insulin (e.g. insulin glargine, insulin detemir, NPH insulin) using one or two daily injections and with three or more daily meal-time insulin injections (e.g. insulin aspart, insulin lispro, insulin glulisine, human insulin) used as bolus insulin therapy * HbA1c maximum 10.0 % by central laboratory analysis * Body Mass Index (BMI) below or equal to 35.0 kg/m\^2 * Ability to self-manage insulin therapy as assessed by confirmation (verbal confirmation at screening visit) of a changed insulin dose in the preceding two months prior to screening * Ability and willingness to adhere to the protocol including performance of self measured plasma glucose (SMPG) profiles and self adjustment of insulin doses Exclusion Criteria: * Use within the last 3 months prior to Visit 1 of any antidiabetic glucose lowering drug other than insulin * Cardiovascular disease, within the last 6 months prior to visit 1, defined as: stroke; decompensated heart failure New York Heart Association (NYHA) class III or IV; myocardial infarction; unstable angina pectoris; or coronary arterial bypass graft or angioplasty * Uncontrolled treated/ untreated severe hypertension (systolic blood pressure above or equal to 180 millimetre (mm) mercury (Hg) and/or diastolic blood pressure above or equal to 100 mmHg) * Pregnancy, breast-feeding, the intention of becoming pregnant or not using adequate contraceptive measures according to local requirements * Cancer and medical history of cancer (except basal cell skin cancer or squamous cell skin cancer)