The present invention relates to novel 5,6-dihydroimidazo[1,5-a]pyrazin-3(2H)-one derivatives as inhibitors of beta-secretase, also known as beta-site amyloid cleaving enzyme, BACE, in particular BACE1 and/or BACE2 (wherein BACE1, is also known as Asp2, or memapsin2 and BACE2 is also known as Asp1, Memapsin 1 or DRAP). The invention is also directed to pharmaceutical compositions comprising such compounds, to processes for preparing such compounds and compositions, and to the use of such compounds and compositions for the prevention and treatment of disorders in which beta-secretase is involved, such as Alzheimer's disease (AD), mild cognitive impairment, senility, dementia, dementia with Lewy bodies, Down's syndrome, dementia associated with stroke, dementia associated with Parkinson's disease, dementia of the Alzheimer's type, dementia associated with beta-amyloid, age-related macular degeneration, type 2 diabetes and other metabolic disorders.