Kallmann's syndrome is a rare disorder which, according to a recent estimate, affects around 1 in 10,000 men and 1 in 70,000 women. People with Kallmann's have an hormonal deficiency which, unless you seek appropriate medical treatment, results in a failure to go through puberty normally. In other words, without treatment you remain sexually underdeveloped and infertile.

Another characteristic of Kallmann's syndrome is an absent sense of smell, or anosmia. Although most people with Kallmann's are anosmic, a small minority are hyposmic, meaning that they have only a very weak sense of smell. Kallmann's syndrome is only one of a group of related diseases. If you are not anosmic or hyposmic and you are having hormone replacement therapy, then you are almost certainly affected by an hormonal disorder other than Kallmann's syndrome.

It is very difficult to diagnose Kallmann's syndrome in a young child. However, alert paediatricians can sometimes detect signs early on, especially if the child cannot smell. The disease is more easily diagnosed in a teenager or adult who has failed to go through puberty and in whom an abnormal sense of smell is observed, but many are too embarrassed about their lack of sexual development and are nervous about visiting their GP. Consequently, there are probably many cases of Kallmann's syndrome that go unreported.