CTD/transmissometer profiles were made on four cruises in the northwest Aegean Sea to study seasonal and spatial distribution patterns of particulate matter (PM). Water samples were filtered to obtain particulate matter concentrations and subsequently to calibrate transmissometer readings. Continental runoff is a major particle source during high river discharge seasons (winter and spring). Resuspended particles predominate in the water column during summer and autumn. Particulate matter distribution patterns consist in well-defined surface, intermediate and bottom nepheloid layers (SNL, INL, and BNL, respectively). The SNL is intense during spring and winter, while it is very weak during summer and autumn. The prevailing wind-driven cyclonic circulation regulates the PM distribution over the shelf, whereas the pycnocline depth controls mainly the vertical PM distribution. The resuspension of modern loosely consolidated sediments, under the forcing of near-bottom currents, forms consistent BNLs over the continental shelf throughout the year. The detachment of these BNLs at the shelf break generates weak INLs, which account for an important shelf-basin transport mechanism during winter and spring. The total particulate standing crop is estimated to be between 484 ¿ 103 and 830 ¿ 103 tons. During summer and autumn, the PM on the shelf results largely from resuspension.