Traditional research on "world cities" tends to develop the idea that large, inter-connected agglomerations can better take advantage of international competition. This suggests that we should observe an increasing concentration of activities in these cities at the expense of smaller ones. Among analyses using measures based on scientific publications, certain studies support this hypothesis. Others however, show that in certain countries such as China, an opposite trend is emerging; the largest cities are undergoing a relative decline in the country's scientific activities. To go beyond this seeming contradiction, this paper provides a global analysis of all countries having papers in Thomson Reuters 'Web of Science' over the period 1987-2007. The addresses -present in each article- were geo-coded and then grouped into agglomerations. The result of our analysis is unambiguous: deconcentration is clearly the dominant trend -both: globally and within countries-, despite some rare exceptions for which explanations are suggested.