This study presents the first comparison of seasonal groundwater storage (GWS) variations derived from GRACE satellite data with groundwater-level measurements in the High Plains Aquifer, USA (450,000 km2). Correlation between seasonal GRACE terrestrial water storage (TWS) and the sum of GWS estimated from field measurements (2,700 wells) and soil moisture (SM) simulated by a land surface model is high (R = 0.82). Correlation between GRACE-derived and measured GWS is also significant (R = 0.58). Seasonal GRACE-derived TWS and GWS changes were detectable (≥ uncertainty) in 7 and 5 out of 9 monitored periods respectively whereas maximum changes (between winter/spring and summer/fall) in TWS and GWS were detectable in all 5 monitored periods. These results show the potential for GRACE to monitor GWS changes in semiarid regions where irrigation pumpage causes large seasonal GWS variations.