Thus, here, we discuss the significant roles of CHI3L1 in the development of cancers (lung, liver, and colon), neurological diseases (Alzheimer’s disease, schizophrenia, etc.), cardiovascular diseases, and rheumatoid arthritis; moreover, we provide some information pertaining to the significance of CHI3L1 in the most common autoimmune disease among Korean children, i.e., atopy. The gene discussed is CHI3L1; the disease is Alzheimer disease.