The authors in this review classify and characterize the major muscle diseases of draught and sport horses with a special focus on those with rhabdomyolysis, and a special form of which occurs in a well-defined endemic region of Transylvania. Muscle disorders significantly reduce the performance of horses, thus causing economic losses due to mortality and morbidity. Various different categorizations exist, based upon objective and anecdotal data. Given the diversity and phenotypic manifestations, conclusive and widely accepted classifications remains to be controversial. There are 3 leading theories like lactic acid accumulation, genetic predisposition; selenium and vitamin E deficiency. Muscle disorders with different aetiology are often present with non-specific clinical signs including: weakness, stiffness, muscle swelling, sweating, and muscle pain. In some cases myoglobinuria, dysphagia, recumbency and death may also occur. In the last section of this paper, the authors shortly describe the exercise induced rhabdomyolysis occurring exclusively in Seklerland's Hargita region.