Failure of a wished-for pregnancy to occur for a period of more than a year during which sexual intercourse has occurred during ovulation. The use of the terms sterility and infertility is justified only after an examination from which it is established that abnormalities are present which make it impossible for pregnancy to come about in the normal fashion. There are many causes of fertility disorders, both in men and in women. The man’s production of healthy sperm cells can be disturbed because a testicle has not descended; the higher temperature then hinders good production of sperm. An attack of mumps after puberty can sometimes affect the sperm-producing tissue. Before puberty, the patient recovers from mumps without any harmful consequences where fertility is concerned. The production of sperm can also suffer through poisoning by heavy metals, smoking and exposure to radiation. Abnormalities in the passage from the testicle hinder the transport of sperm cells. Such abnormalities may be congenital or may result from an operation or inflammation. In women, hormonal disturbances are often the cause of faulty ovulation. This is usually accompanied by an abnormal menstrual cycle. The number of occasions on which ovulation is possible is thereby much reduced. Stress also influences ovulation. The passage of sperm through the cervix can be rendered difficult by an abnormality in the vaginal mucus. Moreover, congenital abnormalities in the oviduct, or constriction arising from scars formed after inflammation, can impede the fertilized ovum’s passage to the uterus. As the above remarks show, the causes of reduced fertility can be of many kinds. The investigation of the causes and their possible treatment can take a long time; both the woman and the man should be involved.