Distribution patterns of live planktic foraminifers are examined at two times of the year, late summer and late winter, through horizontal plankton towing along a NW-SE transect across the West and East Mediterranean Basins and in the Alboran Sea (French oceanographic cruises Vicomed I, II and III, respectively). Foraminiferal production is significantly different in the two sampling periods and across the West and East Mediterranean. Foraminiferal density is higher in winter than summer (e.g. in the western basin: 3700 specimens/1000 m 3 in winter against 200–600 specimens/1000 m 3 in summer). The production, averaged for the two sampling sets, is higher in the Western Basin than in the Eastern one. However, in late summer, peaks of maximal production are observed in the Central Mediterranean (Strait of Sicily and Ionian Basin) (1000 to 2000 specimens/1000 m 3), where the assemblages are dominated by Globigerinoides ruber rosea and G. ruber alba. In the Mediterranean Sea, frontal regions and semipermanent eddies, which are essentially controlled by regional hydrography, represent a significant portion of the regional production. They also elicit a higher diversity of species. Their influence is observed in summer as well as in winter. At the end of summer, the rather shallow mixed layer hosts spinose symbiont-bearing species, such as G. ruber alba, G. ruber rosea, O. universa and G. trilobus. At that season, in the Western Basin, the nutrient content of the mixed layer is generally low, and the surface layer is rapidly nutrient depleted. Summer foraminiferal production remains low at the surface, with respect to the winter production. In the Eastern Basin, late summer and autumn correspond to the “biological spring”. Summer foraminiferal production in surface waters is higher than in winter. But standing crops are lower than in the Western Basin for the same species, at the same period. In summer however, frontal structures and eddies are generally better developed than in winter. In some particular cases (frontal boundaries in the Western Basin; eddies south of Cyprus), nutrients from intermediate layers can be upwelled, through isopycnal or diapycnal mixing, to the photic zone, and allow for secondary blooms. In the Western Basin these blooms favour the development of grazers at depth ( Globorotalia truncatulinoides, G. inflata). South of Cyprus, in the Eastern Basin, oligotrophic conditions promote the development of heterotrophic organisms and predatory foraminifers have higher standing stocks ( G. ruber alba, G. ruber rosea). In winter, the break down of the thermocline combined with deep turbulent mixing in the Northwestern Basin, and the deepening of the mixed layer in the Alboran Sea and along the North African coast, result in increased phytoplankton biomass and favour reproduction and proliferation of species such as G. truncatulinoides or G. inflata. Our observations indicate that the geographic and depth distribution of live foraminiferal species cannot be entirely explained by the general temperature and salinity differences among the different Mediterranean Basins but that they are strongly related to regional hydrographic patterns. Hydrography controls the seasonality and depth of the turbulent mixing (which differ between the Western and the Eastern Basins), the depth of the mixed layer and its seasonal stratification, and the strength of the pycnocline. Nutrient supply and primary production are mostly regulated by these dynamics. One may therefore expect that the species assemblages, on the sea floor and in deep-sea cores, will also correlate to the various hydrographic parameters of the overlying water masses.