Relative performances of available ionospheric models for computing path delay corrections to radar altimeter range data have been assessed using altimeter crossover measurements computed for the single-frequency altimeter measurements collected by Geosat and ERS-1, and for the dual-frequency altimeter measurements collected by TOPEX/POSEIDON. The models studied include IRI-90, IRI-95, and JPL GIM. The models are further compared with the ionospheric delay computed from TOPEX/POSEIDON dual-frequency altimeter data. Crossover analyses indicate that IRI-95 is an improved model over IRI-90 for computing ionospheric delays for all three altimetric satellites during low to medium solar activity periods. It is found that smoothing of the TOPEX/POSEIDON dual-frequency ionospheric correction significantly improved the precision of the TOPEX/POSEIDON data.