Does saline water of Kuroshio origin intrude into the Yellow Sea interior by a persistent mean current through the Yellow Sea Warm Current or by an intermittently generated wind-driven current? This very fundamental question is discussed by analyzing comprehensive conductivity-temperature-depth data collected over the entire southern Yellow Sea basin and by analyzing satellite-tracked drifter trajectories collected in 1996 and 1997. In the southwestern Yellow Sea, relatively saline water (33.0--34.0 psu) persists year-round, implying a northwestward intrusion of Cheju Warm Current water (CWCW). This water is a mixture of saline CWCW, with salinity higher than 34.0 psu, and fresh Yellow Sea waters, with salinity <33.0 psu. During the winter monsoon the mixed water distribution is tongue-shaped, apparently intruding from the CWCW area. At the same time a strong thermohaline front with a horizontal form similar to the Greek letter &Ggr; forms across the southern entrance of the central Yellow Sea trough and separates the mixed water area from the CWCW. During the summer monsoon the CWCW intrusion is weak, and the mixed water that intruded in the previous winter monsoon remains inside the trough as its salinity decreases. In winter, occasional collapses of part of the front on the western side of the trough are observed, presumably in response to an imbalance between northwest currents generated by strong northerly wind bursts and southeast, tide-induced residual currents. Saline water in the frontal zone may then flush into the southwestern Yellow Sea through the collapsed area of the front. We conclude that the YSWC is not a persistent mean current. We also conclude that CWCW may be transported to the southwestern Yellow Sea in winter by the intermittently generated northwest currents on the western slope of the trough, which override the tide-induced residual currents that flow to the southeast in this part of the basin. ¿ 2001 American Geophysical Union