This disease was described by McArdle as an inherited autosomal recessive affection characterized by glicogen storage with normal chain in the skeletal muscles, due to absence of myophosphorylase activity. Under a clinical aspect, excessive fatigability, cramps and myoglobinuria appear following physical exercise. A case of this disease in a 36-year-old male patient is reported. Failure of elevation of venous blood lactate after physical effort under anaerobic conditions, as well as muscle histochemistry, made diagnosis confirmation possible. The authors comment on the differential diagnosis betwen McArdle's disease and the other causes of myoglobinuria, specially phosphofructokinase and carnitine-palmityl-transferase deficiency.