Large-diameter (4 to 6 m) monopiles are often used as foundations for offshore wind turbines. The monopiles are subjected to large horizontal forces and overturning moments and they are traditionally designed based on the p-y curve method. The p-y curves recommended in offshore design regulations are developed for piles with diameters up to approximately 2.0 m and are based on a very limited number of tests. Hence, the method has not been validated for piles with diameters of 4 to 6 m. During the last six years extensive studies on non-slender large-diameter piles in coarse-grained material have been conducted at Aalborg University (AAU) and at the Technical University of Denmark (DTU). The piles have been investigated by means of physical and numerical modelling. The former consists of both centrifuge tests and tests in a so-called pressure tank (1G tests but with an applied overburden pressure). The goal of the work has been to investigate the general behaviour of monopiles for nowadays offshore wind turbines and to revise the p-y curves for piles in sand in order to account for diameter on the response of monopiles subjected to both static and cyclic loads. The paper summarizes and compares the results of the studies conducted at AAU and DTU.