Background and objectives: Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and leukoencephalopathy (CADASIL) is the most frequent genetic cerebrovascular disease. The clinical aspects of the disease in relation to the various types of lesions on MRI vary widely within families but also between different cohorts reported worldwide. Many limitations prevent comparison of imaging data obtained with different scanners and sequences in different patients cohorts. We aimed to develop and validate a simple tool to inventory quickly the key MRI features in CADASIL to compare imaging data across different populations. Methods: The Inventory Tool (CADA-MRIT) was designed by consensus after repeated expert meetings. It consisted of eleven imaging items to assess periventricular, deep, and superficial white matter hyperintensity (WMH), lacunes, cerebral microbleeds (CMB), centrum semiovale and basal ganglia dilated perivascular spaces (dPVS), superficial and deep atrophy, large infarcts, and macrobleeds. The reliability, clinical relevance, and time-effectiveness of CADA-MRIT were assessed using data from three independent patient cohorts. Results: Imaging data from 671 CADASIL patients (440 from France, 119 from Germany and 112 from Taiwan) were analyzed. Their mean age was 53.4 ± 12.2 years, 54.5% were women, 56.2% had stroke, and 31.1% had migraine with aura. Any lacune was present in at least 70% of individuals, whereas CMB occurred in 83% of patients from the Asian cohort and in only 35% of European patients. CADA-MRIT scores obtained for WMH, CMB and dPVS were comparable regardless of the scanner or sequence used (weighted κ > 0.60). Intrarater and interrater agreements were good to very good (weighted κ > 0.60). Global WMH and atrophy scores correlated strongly with accurate volumetric quantification of WMH or brain parenchymal fraction (Pearson r > 0.60). Different imaging scores were significantly associated with the main clinical manifestations of the disease. The time for evaluating one patient was around 2-3 minutes. Discussion: The CADA-MRIT is an easy-to-use tool for analyzing and comparing the most frequent MRI lesions of CADASIL across different populations. This instrument is reliable. It can be used with different imaging sequences or scanners. It also provides clinically relevant scores in a very short time for completion.