Two types of scour can be identified at piles supporting offshore structures: (1) Erosion of the sea bottom (sea-bottom scour) at obstructions due to oscillatory waves and unidirectional currents (2) Loss of soil around a pile due to the cyclic deflections of the pile under wave forces. The second type (pile scour) is associated with cohesive soils and is the subject of this study. Observations during onshore testing have revealed that the loss of lateral capacity of a pile in cohesive soils is due principally to the creation of a gap at the pile-soil interface and to the subsequent ejection of water from the gap as the space opens and closes during the cyclic loading. The paper describes the phenomenon of pile scour, presents the details of a laboratory test to investigate the scour potential of various soils, discusses the significant findings of a research study and indicates the influence of pile scour on the design of laterally loaded piles for offshore structures.