The interleaving of water masses across the equator is a predominant feature in the upper equatorial Pacific Ocean. The interleaving is thought to promote lateral mixing and impact on the basin-wide dynamics of the equatorial ocean. Hydrographic observations in the western equatorial Pacific have, for the first time, provided the three-dimensional structure of the interleaving layers. Though the details are different, the general characteristics of the vertical and meridional structure are consistent with previous observations. The layers show a remarkably long zonal coherence, with individual layer being in excess of 700 km in length, which are matched only by intrusions in the Arctic. The large zonal coherence is further evidence of the potential importance of the interleaving, and points to the need to include the process in models of the equatorial ocean.