The seasonal and global distributions of laminae in nitrous oxide (N2O), a long-lived tropospheric source gas, are examined in a multi-year, three-dimensional model simulation. The frequency of laminae occurrences is described as a function of geographical location and season. Enhanced laminae occurrence is found in the midlatitude surf zones of both hemispheres, but there are zonal asymmetries, especially in the northern hemisphere. In boreal winter and spring, laminae intruding from mid-latitudes into the deep tropics are found across the Pacific Ocean, on the southern flank of the Aleutian High. A quiet zone, free of laminae, lies on the summer side of the equator, and separates the winter from the summer stratosphere. It coincides in latitude with the location of the N2O low-latitude maximum. High laminae occurrences are again found in the extratropics of the summer hemisphere. ¿ 2000 American Geophysical Union