Kallmann's syndrome is a congenital hormonal condition characterised by the failure of an individual to enter puberty. It is a form of hypogonadotrophic hypogonadism.

The underlying cause is a failure in the communication pathways within the body that should operate in order to initiate puberty at the correct time. In particular it is a failure of communication between two structures inside the brain called the hypothalamus and the anterior pituitary gland.

This failure of communication results in the sex organs or gonads (testes or ovaries) not maturing in the usual manner during puberty.