Latent autoimmune diabetes in the adult (LADA) is a slowly progressive form of autoimmune diabetes, characterized by diabetes-associated autoantibody positivity. A recent hypothesis proposes that LADA consists of a heterogeneous population, wherein several subgroups can be identified based on their autoimmune status. A systematic review of the literature was carried out to appraise whether the clinical characteristics of LADA patients correlate with the titre and numbers of diabetes-associated autoantibodies. We found that the simultaneous presence of multiple autoantibodies and/or a high-titre anti-glutamic acid decarboxylase (GAD)--compared with single and low-titre autoantibody--is associated with an early age of onset, low fasting C-peptide values as a marker of reduced pancreatic B-cell function, a high predictive value for future insulin requirement, the presence of other autoimmune disorders, a low prevalence of markers of the metabolic syndrome including high body mass index, hypertension and dyslipidaemia, and a high prevalence of the genotype known to increase the risk of Type 1 diabetes. We propose a more continuous classification of diabetes mellitus, based on the finding that the clinical characteristics gradually change from classic Type 1 diabetes to LADA and finally to Type 2 diabetes. Future studies should focus on determining optimal cut-off points of anti-GAD for differentiating clinically relevant diabetes mellitus subgroups.