N-methyl-D-aspartate receptor (NMDAR) encephalitis is the most common autoimmune encephalitis due to autoantibodies against neuronal surface antigens, can affect both children and adults, leading to neurological and neuropsychological sequelae. However, it is potentially treatable and the prompt start of immunotherapy associates with better prognosis. Conversely, misdiagnosis can be harmful. The detection of NMDAR antibodies in serum and cerebrospinal fluid plays a pivotal role in the diagnostic work-up. Reliable methods for NMDAR antibody detection are thus fundamental to assure accurate diagnosis and allow early treatments. Areas covered: This review recapitulates the pathogenic mechanisms of NMDAR encephalitis as a model of antibody mediated synaptopathy, and gives insights into the related state-of-the-art laboratory testing. The differences in clinical presentations, tumor associations and responses to treatments between adults and children are also described. Expert commentary: The relevance of NMDAR encephalitis has placed neuroimmunology laboratories in a crucial position, but methods for NMDAR antibody detection are awaiting thorough and consensus-based standardizations. In the next few years, this process, along with novel insights into the pathogenic mechanisms, could improve the disease management and clarify the still pending role of NMDAR antibodies in healthy people and in other more common neuropsychiatric disorders.