The data of laser sensing of the vertical aerosol distribution obtained at Siberian Lidar Station of the Institute of Atmospheric Optics, Tomsk (56.5 degrees N, 85.1 degrees E), Russia in 1986-1995 are analyzed. The data are presented in the form of the scattering ratio R (H), the aerosol backscattering coefficient beta(pi)(a)(H), and the integrated aerosol backscattering coefficient between 15 and 30 km Sigma beta(pi)(a) at the wavelength lambda = 532 nm. During the period from summer 1986 to summer 1991, Sigma beta(pi)(a) varied in the range 0.8 x 10(-4)-3 x 10(-4) sr(-1). Average profiles of R(H) and beta(pi)(a)(H) for the main seasons, the annual behaviour of the altitude of the peak scattering ratio and of the tropopause height, and the eigenvectors of the correlation matrix of R (H) are also presented for this period. In succeeding years, the behavior of the stratospheric aerosol layer (SAL) was primarily determined by the Pinatubo volcanic aerosol. Based on an analysis of the scattering ratio profiles, the formation of the vertical volcanic aerosol stratification above Tomsk is demonstrated. The maximum values of Sigma beta(pi)(a) approximate to 4 x 10(-3) sr(-1), caused by the volcanic aerosol, were observed in January-February 1992. Between 15 and 30 km, the 1/e-decay time of the stratospheric volcanic aerosol was 357 +/- 37 days. Lidar measurements carried out on certain days simultaneously at lambda = 532, 353, and 628 nm allowed us to investigate the transformation of the exponent A(H) that characterizes the spectral dependence of the volcanic aerosol backscattering coefficient in the wavelength range 353-532 nm and to estimate the geometric cross section of particles S(r).