Kallmann syndrome (KS) is a rare genetic hormonal condition that is characterised by a failure to start or fully complete puberty. It is also associated with a lack of sense of smell (anosmia).

Kallmann syndrome belongs to a group of conditions known as congenital hypogonadotropic hypogonadism (CHH).

Kallmann syndrome is name given to any case of CHH that is accompanied by anosmia.

Kallmann syndrome and CHH affects both men and women but is diagnosed more often in men. The actual incidence is unknown but thought to be in the region between 1 in 10,000 and 1 in 50,000.

The condition is most often present from birth (congenital) but it can occur in adulthood, after normal puberty in both males and females.

The congenital forms of the condition result in a disruption in the normal development at puberty. This disruption can either be complete or partial.