Microwave radiometers form an integral part of satellite altimetry. The long-term stability of the radiometer measurements is as important to the accurate determination of sea level rise as is the long-term stability of the altimeter instrument. However, the radiometer stability has been largely taken for granted. Detailed long-term study of the brightness temperatures of ERS-1, ERS-2, TOPEX/Poseidon, GFO, Jason-1, and Envisat, reveals that all but two exhibit significant drifts or jumps in the brightness temperatures measured by at least one of their frequency channels. This poses serious challenges on the estimation of sea level change to better than 0.2 mm/yr. This article provides updates to corrections proposed in previous studies and illustrates the sensitivity of sea level change estimates to the long-term stability of the radiometers accompanying the satellite altimeters, as well as the altimeter backscatter coefficient.