The Tropical Rainfall Measuring Mission (TRMM) is the first satellite mission devoted solely to rainfall measurements and provides unprecedented spatially and temporally collocated multi-sensor data for the tropical and subtropical regions of the world. An evaluation of rainfall retrieval techniques is important for highlighting limitations, strengths and differences between rainfall climatologies, before application to hydrological problems. This study aims to compare rainfall climatologies, based on a range of rainfall estimation algorithms, for June, July and August 1999 from the first active radar in space, the Precipitation Radar and the TRMM Microwave Imager. Another important aspect of this work is to provide initial regional error estimates from algorithms, albeit based on limited validation data. The passive microwave data is first optimised through application of four Frequency Difference and three Polarization Corrected Temperature algorithms. The Precipitation Radar data consists of the average rain rate between 2km and 4km from TRMM Science Data and Information System and is calibrated with the passive microwave data through the Histogram Matching Technique to provide rain rate boundaries. Qualitative comparisons for coincident only situations highlight regional discrepancies between the passive microwave algorithms and the PR analysis. These regional differences are attributed mainly to surface effects and different rainfall regimes. Results indicate a need for regional calibration that is conducted for specific regions to derive varying rain rate optimised passive microwave relationships. An investigation into the diurnal cycle of rainfall for each algorithm has also been conducted and is found to be more subdued over the ocean compared to the land.