This paper describes the validation of ozone profiles from the Polar Ozone and Aerosol Measurement (POAM) III instrument. POAM III O3 is measured with 1-km vertical resolution throughout most of the stratosphere and random errors of ~5%. It is shown that sunspots do not significantly affect the POAM O3 retrievals, nor do polar stratospheric clouds, except under rarely encountered, extreme conditions of very low O3 and exceptionally high aerosol extinction. A statistical analysis is presented of comparisons between coincident measurements from POAM III and ozonesondes, the Halogen Occultation Experiment (HALOE) and the Stratospheric Aerosol and Gas Experiment (SAGE) II. On average, POAM III O3 profiles agree to within ¿5% with these correlative data from 13 to 60 km. There is a suggestion that from 30 to 60 km POAM III sunrise data might be biased slightly low (<5%) relative to POAM sunset data. There is evidence that POAM III has a high bias of up to ~0.1 ppmv from 10 to 12 km, and that this bias might stem, in part, from errors in the retrieval of aerosol extinction at 0.6 ¿m, the primary O3 absorption wavelength in the POAM retrievals. Below 10 km the POAM III data agree with coincident sonde measurements to better than 0.05 ppmv on average, which can correspond to large relative differences of more than +30% at 8--9 km and -100% at 5 km. We conclude that the POAM III profiles are highly accurate and adequate for quantitative scientific studies.