ATLAS, the Airborne Tunable Laser Absorption Spectrometer, was used to measure nitrous oxide in the 1987 Airborne Antarctic Ozone Experiment (AAOE) and in the 1989 Airborne Arctic Stratospheric Expedition (AASE). After the AASE, a detailed study of the ATLAS characteristics was undertaken to quantify the error inherent in the in situ measurement of atmospheric N2O. Using the latest calibration of the ATLAS (June 1989) and incorporating the recognized errors arising in the flight environment of ATLAS, we have established that for both the AASE and the AAOE most of the acquired N2O data sets are accurate to ¿10% (2 sigma). Data from two of the earlier AAOE flights had a larger uncertainty. ¿ American Geophysical Union 1990