Khat (Catha edulis Forsk.), known in Somalia as "qaad" or "jaad", is a plant whose leaves and stem tips are chewed for their stimulating effect. From the Harar area, khat has been introduced at different times into the present day territories of Somalia, Djibouti, South and North Yemen, Kenya, Madagascar, Tanzania and down to south eastern Africa. The plant, which belongs to the Celestraceae family, grows wild at altitudes of 1500-2000 m above sea level. Among the various compounds present in the plant (more than forty alkaloids, glycosides, tannins, terpenoids, etc.), two phenylalkylamines, namely cathine [+)-norpseudoephedrine) and cathinone [-)S-o-aminopropiophenone) seem to account mostly for the effect. The consumers get a feeling of well-being, mental alertness and excitement. The after effects are usually insomnia, numbness and lack of concentration. The excessive use of khat may create considerable problems of social, health and economic nature. These problems have been summarily reviewed. Khat chewing started at different times in different parts of Somalia. Since World War II, the prevalence of the practice has continuously increased and no social group is excluded. An epidemiological research to compare Northern and Southern regions of Somalia and to obtain a rough estimate of prevalence, definition of social characteristics of the groups of consumers, specification of the motivations, patterns of use and effects during and after consumption has been conducted. Consumers and non-consumers (7485 people) were randomly interviewed in the two regions. Khat consumption in relation to sex, age, occupation and grade of education is presented.