Type 1 diabetes mellitus (DM1) is an autoimmune disease characterized by a lack of insulin production by beta pancreatic cells. Immunological mechanisms play a key role in DM1 physiopathology, even in asymptomatic patients where different autoantibodies directed against several components of beta cells have been found. The human leucocitary antigen, islet cells autoantibodies, insulin autoantibodies, glutamic acid decarboxilase autoantibodies and the rapid intravenous glucose tolerance test can be used to identify individuals with high risk for developing DM1. Ganglioside GM2-1 and the tyrosine phosphatase enzyme (IA2/ICA512) antigens determination are also employed to assess DM1 individual risk. This risk is significantly higher when three or four autoantibodies are found. Nowadays, the islet cell autoantibodies are employed as markers for DM1. This work analyzes the immunological aspects related to DM1, and highlights recent developments in this field.