The retrieval of geophysical parameters of the Earth and its atmosphere from satellite observations fundamentally relies upon the accuracy of the measurements. The growth in communication technologies has led to the exploitation of regions of the electromagnetic spectrum hitherto primarily used for Earth observation. This article describes and maps the distribution of radio frequency interference in the microwave portion of the spectrum using data from the Advanced Scanning Microwave Radiometer. The frequencies most affected are primarily the 6.925 and 10.65 GHz channels, although there is some evidence of contamination at the higher frequency of 18.7 GHz. The amount of contamination is seen to differ across the globe due to regional legislation. Regions of interference can be found by identifying measurements where horizontal polarized brightness temperatures exceed that of vertically polarized brightness temperatures. These regions are generally well matched with the distribution of global population, although some exceptions exist and are identified. At present there is little significant interference over the oceans.