In this review article on the origin of HIV, we start from a historical fact which involved physicians from Liège working in Belgian Congo: the vaccination against polio of hundreds of thousands of Congolese between 1957 and 1960. We explain the genesis of an alternative hypothesis postulating that this campaign was at the origin of HIV pandemy. We show that the hypothesis is unfounded in view of genetic and epidemiological evidence on the one hand and after thorough examination of the activity reports of the Laboratoire Médical de Stanleyville on the other. In the second part of the article, we analyse the importance of other factors which might have contributed to the emergence of the pandemy. Some of these are clearly iatrogenic such as the prophylactic injections of pentamidine against trypanosomiasis, others are of demographic and sociological nature. All of them have a direct link with colonisation.