SummaryA demonstrative instance of epidemic myalgia is described. Present knowledge about this nosological entity is stated. Clinical symptoms and differential diagnosis especially are studied in particular. Stress is laid on the importance of the knowledge of Bornholm myalgia :—nosagraphic importance,—importance of diagnosis (elimination of diagnostic errors that may cause prejudice and lead, for instance, to useless operations),—pronostic importance (usually favourable evolution despite diabolical character of the disease).