Genital ulcer disease as a risk factor for HIV transmission has become apparent in the fight against AIDS. In poor communities in developing countries with people living under low hygienic conditions chancroid is often reported to be the most common form of genital ulcer. It is caused by Haemophilus ducreyi; a fastidious bacterium, notoriously difficult to grow in the laboratory. Apart from a few small micro-epidemics from time to time the disease, which has interesting immunological aspects, is now rare and almost forgotten in most industrialized countries. This may be part of the reason why there is no simple and inexpensive diagnostic test available yet that would be useful in the low-resource settings where chancroid is prevalent. The present review focuses on the diagnosis and pathogenesis of chancroid.