The record of lidar observations of the stratospheric aerosol layer at Garmisch-Partenkirchen from 1976 to 1999 reflects the natural variability of this layer at northern midlatitudes. The time series of particle backscatter measurements is characterized by volcanic perturbations in the 1980s and 1990s and has captured three periods of low aerosol loading. The discussion of unperturbed and perturbed periods is based on backscatter data and on particle mass and optical depth data derived from backscatter measurements. Similar nonvolcanic or background conditions were observed in the late 1970s and late 1990s. Outstanding events were the perturbations after the tropical eruptions of El Chich¿n, Mexico, in 1982 and Pinatubo, Philippines, in 1991. When analyzing the decay in stratospheric aerosol loading caused by these two major perturbations, patterns emerge that differ distinctly from each other when starting the comparison with the year of the respective eruption. The observed differences disappear after synchronizing the respective phases of the equatorial quasi-biennial oscillation (QBO) following these two eruptions. This occurs when the Pinatubo decay of 1993--1995 is compared with the El Chich¿n decay of 1983--1985. Similar QBO phases suggest that in the winters 1982/1983, 1984/1985, 1992/1993, and 1994/1995, comparable transport patterns out of the tropics lead to increased aerosol concentrations at northern midlatitudes as observed by lidar at Garmisch-Partenkirchen.