Six hundred and eighty one diagnoses were established by means of cell culture and chromosome analysis on amniotic fluid obtained either by late amniocentesis or at the time of therapeutic abortion. Each prenatal diagnosis involved: 1. Genetic consultation. 2. Supervision of the pregnancy before amniocentesis. 3. Amniocentesis in the obstetric department. 4. Confirmation of the diagnosis when an abnormality of the foetus was discolvered. 5. Supervision of the pregnancy following the anmiocentesis and examination of the infant at birth and during the first year of life. The indications for chromosome studies and the results are discussed.