71 cases of mitral valve prolapse (MVP) in the child and adolescent with an age range of 3 to 20 years were reviewed. The clinical symptoms, electrocardiography and catheter and angiographic data of this mitral abnormality were analysed. A systematic study of the electrocardiogram showed a tendency to spasmophilia in 68% of cases. The serum calcium, phosphate and magnesium levels were normal in 90 to 95% of patients. A reduced erythrocytic magnesium level seems to have been found in some patients. It is interesting to observe the similarity between the clinical signs in MVP and in spasmophilia. These clinical, biochemical and electrocardiographical results justify the systematic investigation of children and adolescents with MVP, with a view to the diagnosis of spasmophilia.