A consensus conference was held to establish diagnostic criteria for multiple system atrophy (MSA). The disease is characterized by four domains: autonomic failure/urinary dysfunction, parkinsonism, cerebellar ataxia, and corticospinal dysfunction. Diagnosis of possible MSA requires one criterion plus two features from separate domains. Probable MSA requires autonomic failure/urinary dysfunction plus poor levodopa-responsive parkinsonism or cerebellar ataxia. Definite MSA requires pathological confirmation. MSA is a progressive neurodegenerative disorder with no known cause, affecting both sexes, typically beginning in middle age. It causes parkinsonism, cerebellar, autonomic, urinary, and pyramidal dysfunction. Clinical features include bradykinesia, rigidity, postural instability, hypokinetic speech, tremor, ataxia, orthostatic hypotension, erectile dysfunction, constipation, and urinary symptoms. Diagnosis is primarily clinical, though laboratory tests may support it. Neuropathological changes include glial cytoplasmic inclusions (GCIs) in various brain structures. GCIs are ubiquitin-, tau-, and α-synuclein-positive oligodendroglial inclusions. The conference established three diagnostic categories: definite, probable, and possible. Definite MSA requires neuropathological confirmation. Probable or possible MSA is diagnosed based on clinical features. The term "Shy Drager syndrome" is discouraged, and patients are classified as MSA-P (parkinsonian features) or MSA-C (cerebellar features). The guidelines were developed to improve diagnosis and differentiate MSA from Parkinson's disease and PSP. They are not yet validated and may require modification. Laboratory tests such as autonomic function tests, sphincter EMG, and MRI may support diagnosis but are not essential. The guidelines aim to provide a standardized approach to diagnosing MSA.A consensus conference was held to establish diagnostic criteria for multiple system atrophy (MSA). The disease is characterized by four domains: autonomic failure/urinary dysfunction, parkinsonism, cerebellar ataxia, and corticospinal dysfunction. Diagnosis of possible MSA requires one criterion plus two features from separate domains. Probable MSA requires autonomic failure/urinary dysfunction plus poor levodopa-responsive parkinsonism or cerebellar ataxia. Definite MSA requires pathological confirmation. MSA is a progressive neurodegenerative disorder with no known cause, affecting both sexes, typically beginning in middle age. It causes parkinsonism, cerebellar, autonomic, urinary, and pyramidal dysfunction. Clinical features include bradykinesia, rigidity, postural instability, hypokinetic speech, tremor, ataxia, orthostatic hypotension, erectile dysfunction, constipation, and urinary symptoms. Diagnosis is primarily clinical, though laboratory tests may support it. Neuropathological changes include glial cytoplasmic inclusions (GCIs) in various brain structures. GCIs are ubiquitin-, tau-, and α-synuclein-positive oligodendroglial inclusions. The conference established three diagnostic categories: definite, probable, and possible. Definite MSA requires neuropathological confirmation. Probable or possible MSA is diagnosed based on clinical features. The term "Shy Drager syndrome" is discouraged, and patients are classified as MSA-P (parkinsonian features) or MSA-C (cerebellar features). The guidelines were developed to improve diagnosis and differentiate MSA from Parkinson's disease and PSP. They are not yet validated and may require modification. Laboratory tests such as autonomic function tests, sphincter EMG, and MRI may support diagnosis but are not essential. The guidelines aim to provide a standardized approach to diagnosing MSA.