Cortical superficial siderosis (cSS) is known to be an imaging feature of cerebral amyloid angiopathy (CAA), and has prognostic relevance in patients with this condition. However, the relevance of this marker in other forms of small vessel disease is unclear. In a recent study, investigators carried out MRI in 364 patients with CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), 100 patients with CAA, and 372 healthy controls. Most imaging features, including white matter hyperintensities and cerebral microbleeds, were similar in the CADASIL and CAA patients, but cSS was only found in the patients with CAA. This finding suggests that the presence of cSS is strongly indicative of CAA in individuals with other features of small vessel disease.