Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by motoneuron degeneration. Increasing evidence suggests immune system involvement in ALS pathogenesis but information about peripheral blood characteristics has been lacking. We evaluated hematological and morphological parameters in peripheral blood of G93A SOD1 mice. A significant decrease in white blood cells was found at the end stage of disease. The lymphocyte reduction may suggest immunodeficiency in ALS. Spontaneously forming rosettes with autologous erythrocytes were noted in approximately 28% of lymphocytes in SOD1 mice. To our knowledge, this is the first study characterizing hematology and revealing autorosettes in the SOD1 mouse model of ALS at the terminal phase of disease.