Due to the progressive ageing of the population and to the age-associated increase in its incidence, Alzheimer disease (AD) will become in near future one of the major challenges that healthcare systems will have to face with in developed countries. Since the pathophysiological process of AD is thought to begin many years before the clinical diagnosis of dementia, in theory there is an opportunity for preventive therapeutic interventions. In recent years, there has been a growing interest, supported by a large number of experimental and epidemiological studies, in the beneficial effects of some natural compounds inpreventing various age-related pathologic conditions, including brain aging and neurodegeneration. Homotaurine, a small aminosulfonate compound that is present in different species of marine red algae, has been shown, in both in vitro and in vivo models, to provide a relevant neuroprotective effect by its specific anti-amyloid activity and by its GABAa receptor affinity. The therapeutic efficacy of homotaurine in AD has been investigated in a pivotal Phase III clinical study that did not reach its pre-defined primary endpoints. However, post-hoc analyses have shown positive and significant effects of homotaurine on secondary endpoints and subgroups of patients, including a reduction in hippocampal volume loss and lower decline in memory function in the overall cohort, as well as a reduction in global cognitive decline in APOE4 allele carriers,suggesting a disease-modifying effects. In this review, we will examine the preclinical and clinical evidence supporting the potential role of homotaurine as a promising candidate for both primary and secondary prevention of AD.