To identify the propagation mode of ULF waves in the magnetosphere, observational determination of their amplitude and phase structure is necessary. Despite the fact that Pc 3 pulsations are observed at various latitudes, no systematic studies of the phase and amplitude structure of Pc 3 over a wide range of latitudes have been done. Using magnetic field data from the Western Pacific magnetometer array centered at 210¿ geomagnetic longitude and from the Geotail satellite, we present the latitudinal structure of a Pc 3 pulsation event that occurred on October 17--18, 1992. During this event, Geotail was located in the dayside magnetosphere at a radial distance of ~8RE and observed tailward propagating fast-mode magnetosonic waves in the Pc 3 band [Takahashi et al., 1994b>. Pulsations observed at the ground stations, also on the dayside, exhibit dynamic spectra similar to those observed from Geotail. Spectral analyses of the ground data reveal that the pulsations are often coherent from L~1 to L~6. Furthermore, the phase of the pulsations varies with L in a complex manner: at low-latitude stations in the L range between 1.1 and 2.9, there is little phase delay; at a high-latitude station (L=5.5) the phase relative to low latitudes is ~180¿; and at an equatorial station (L=1.01), the phase relative to low latitudes is ~150¿. The pulsation amplitude is at an overall maximum at the highest-latitude station of the magnetometer array, but two additional maxima occur at L~1 and L~2.1. We discuss these observations in terms of MHD wave propagation effects in the magnetosphere.¿ 1997 American Geophysical Union