Measurements of lidar-integrated backscatter and Sun photometer optical thickness made at Mauna Loa, Hawaii (19.5 ¿N), were used to compute the bulk columnar value of the extinction-to-backscatter ratio Sc of stratospheric aerosol during a period of major stratospheric aerosol contamination following the eruption of El Chich¿n (Mexico, 17.3 ¿N, March--April 1982). Values of Sc were also calculated using observations of integrated backscatter and aerosol optical thickness collected from various sources in the northern midlatitude region. The calculated values of Sc were found to range between 40 and 70 sr at a wavelength of 0.694 μm during periods when high and moderate stratospheric aerosol concentrations were observed. Variations of Sc with time of approximately 20--30% are noted in the results. Similar Sc results obtained by other investigators are compared with the results of this investigation. Overall, the agreement among the various results was found to be consistent within their uncertainties. Values of Sc were also calculated for the stratospheric aerosol from the eruption of Mount Pinatubo (Philippines, 15 ¿N, June 1991). The Mount Pinatubo results were about 15% lower than the El Chich¿n results during their early stages. Differences between the El Chich¿n and the Pinatubo results are within their error bounds. ¿ 1998 American Geophysical Union