A deterministic model for atmospheric longwave radiation transfer was used with climatological data to predict the mean monthly zonal (10¿ latitudinal zones) longwave radiation budget at the Earth's surface and at the top of the atmosphere for the Northern Hemisphere. The climatological data were obtained from the International Satellite Cloud Climatology Project (1983--1990), and from the National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis Project. The model's outgoing fluxes agree within 4 W m-2, on average, with the corresponding values determined from the Earth Radiation Budget Experiment (1985--1989) satellite data. The validation of the model for the top-of-atmosphere radiation budget allows one to obtain a better understanding of the important processes that govern the transfer of the longwave radiation for each season and zone. At the surface, validation of the predicted downwelling radiation is difficult owing to the lack of extensive ground-based measurements. However, we have made intercomparisons with other model predictions and with ground-based measurements that were available. The predictions of the model for the surface longwave radiation budget provide a measure against which simpler algorithms, derived from ground-based measurements, can be compared and used to convert satellite climatologies to a globally distributed surface longwave radiation budget for climatic studies. ¿ 1999 American Geophysical Union