Migration of skilled health workers from sub-Saharan African countries has significantly increased in this century, with most countries becoming sources of migrants. Despite the growing problem of health worker migration for the effective functioning of health care systems there is a remarkable paucity and incompleteness of data. Hence, it is difficult to determine the real extent of migration from, and within, Africa, and thus develop effective forecasting or remedial policies. This global overview and the most comprehensive data indicate that the key destinations remain the USA and the UK, and that major sources are South Africa and Nigeria, but in both contexts there is now greater diversity. Migrants move primarily for economic reasons, and increasingly choose health careers because they offer migration prospects. Migration has been at considerable economic cost, it has depleted workforces, diminished the effectiveness of health care delivery and reduced the morale of the remaining workforce. Countries have sought to implement national policies to manage migration, mitigate its harmful impacts and strengthen African health care systems. Recipient countries have been reluctant to establish effective ethical codes of recruitment practice, or other forms of compensation or technology transfer, hence migration is likely to increase further in the future, diminishing the possibility of achieving the United Nations millennium development goals and exacerbating existing inequalities in access to adequate health care.