Measurements of stratospheric nitrous oxide made by the Improved Stratospheric and Mesospheric Sounder (ISAMS) during the period 28 October 1991–18 January 1992 are presented. The data are consistent with the dynamical fields at the time, and are in extremely good qualitative agreement with similar data from the Nimbus-7 SAMS and the Upper Atmosphere Research Satellite (UARS) Cryogenic Limb Array Etalon Spectrometer (CLAES) instruments, although in some regions the values are higher than have been obtained elsewhere. A major problem in the retrieval of the data has been contamination of the measured signal by aerosol emitted during the Mount Pinatubo eruption of June 1991. Despite the uncertainty in the values, the ISAMS N2O measurements provide a unique opportunity to study the synoptic evolution of a long-lived chemical tracer throughout the early winter, with near-continuous high-resolution measurements. The zonally averaged data are shown, as well as the measurements in the Northern Hemisphere on the 1150-K isentropic surface, with reference to temperature and wind fields from the same period derived also from ISAMS measurements. Finally, along-track cross sections are shown, which illustrate in greater detail the vertical and horizontal structure of the northern winter vortex region.