Inclusion Criteria:  Male or female aged greater than or equal to 18 years at the time of signing informed consent. Diagnosed with type 1 diabetes mellitus greater than or equal to 1 year prior to the day of screening. Treated with multiple daily insulin injections (basal and bolus insulin analogue regimes) greater than or equal to 1 year prior to the day of screening. HbA1c below10% at screening visit based on analysis from central laboratory.  Exclusion Criteria:  Myocardial infarction, stroke, hospitalization for unstable angina pectoris or transient ischaemic attack within 180 days prior to the day of screening. Chronic heart failure classified as New York Heart Association (NYHA) Class IV at screening. Anticipated initiation or change in concomitant medications (for more than 14 consecutive days) known to affect weight or glucose metabolism (e.g. treatment with orlistat, thyroid hormones, or corticosteroids). Uncontrolled and potentially unstable diabetic retinopathy or maculopathy. Verified by a fundus examination performed within the past 90 days prior to screening or in the period between screening and randomisation. Pharmacological pupil-dilation is a requirement unless using a digital fundus photography camera specified for non-dilated examination.