Some problems concerning the data on immigrants from Sub-Saharan Africa collected in the official French survey on geographical mobility and social integration being conducted jointly by INED and INSEE are examined. The issue concerns the allocation of immigrants to the appropriate ethnic group and the differences between the problems faced by the children of immigrants born in France and those facing the more recent immigrants who may be from the same ethnic group. The author concludes that the survey will probably be more relevant to the study of the latest wave of migrants from Africa than to the study of earlier migrations.