Regarding cardiovascular (CV) risk, patients with type 1 diabetes mellitus (T1D) are a heterogeneous population with CV risk ranging from low to very high. For personalized prevention strategies, screening for subclinical atherosclerosis may be of clinical significance. However, more data is needed. Our study aimed to describe the prevalence of prognostically significant findings on invasive coronary artery examination in patients with subclinical atherosclerosis determined by non-invasive examination of the carotid and coronary arteries. Patients with T1D for at least 10 years, without a prior history of atherosclerotic CV disease or target organ damage, followed at a large tertiary hospital were enrolled. Non-invasive examinations included carotid ultrasound for carotid plaque detection and a CT for coronary artery calcium (CAC) score evaluation. Patients with the presence of ≥2 carotid plaques and/or CAC score of ≥400 were classified as very high risk (VHR). These VHR patients were subsequently evaluated using invasive coronary angiography (ICA) for the presence of obstructive coronary artery disease (CAD) and intracoronary optical coherence tomography (OCT) for the presence of thin-cap fibroatheroma (TCFA) and very high-risk plaque. Moreover, hemodynamic stenosis relevance was assessed by the vessel fraction flow ratio (vFFR). Sixty-two T1D patients aged 50.1±12.7 years, 53 % women were enrolled. The criteria of VHR were fulfilled in 12/62 (19.4 %) patients, of which 6 (50 % of VHR) had both CAC≥400 and at least 2 atherosclerotic plaques in the carotid arteries, one patient (8 % of the VHR) fulfilled only the CAC criteria and 5 (42 % of VHR) only the carotid criteria. The median CAC score of the VHR group was 606.3 (175.3-1515) and the mean number of carotid plaques was 2.75±1.06. ICA showed obstructive CAD in 5/12 (41.7 %) patients, and 3/12 (25 %) had vFFR-positive lesions. Using OCT, TCFA was present in 7/12 (58.3 %) and a very high-risk plaque in 4/12 (33.3 %) patients. Among asymptomatic patients with T1D, the combination of coronary artery calcium score and carotid ultrasound identifies a very high-risk group, in which 58.3 % of patients had a thin-cap fibroatheroma and 33.3 % of patients had a very high-risk plaque. Patients identified by these non-invasive techniques may benefit from intensive risk factors management.