Anaplastic large cell lymphoma (ALCL) is a type of non-Hodgkin lymphoma composed of CD30-positive cells. Anaplastic lymphoma kinase (ALK) -1 positive ALCL frequently involves both lymph nodes and extranodal sites. While primary extranodal involvement of ALK-1 negative ALCL is rare, this case is unique in that it is a case of primary ALK-1 negative ALCL of the brain. A 79-year-old man presented with dementia-like symptoms. Neuroimaging revealed a well-enhanced mass in the left parieto-occipital region. The tumor was excised and histological diagnosis of primary ALK-1-negative ALCL was made. Primary ALK-1-negative ALCL in this case showed aggressive clinical behavior and fatal outcome. It is of great importance to avoid any delay in reaching an accurate diagnosis, as even primary ALCL of the brain is too seldom suspected clinically.