The characterization of the vertical turbulence distribution on an astronomical site should be based on statistical behaviour, as it is required for other parameters in site testing. We present the statistical results of the optical-turbulence profiles at the Roque de los Muchachos and Teide observatories at the Canary Islands (Spain). The data were obtained using the generalized scintillation detection and ranging technique at the 1m Jacobus Kapteyn Telescope and 1.5m Carlos Sánchez Telescope. Statistical results are based on 68 nights in 2004 and 38 nights in 2005 of measurements at the Roque de los Muchachos observatory (La Palma) and 27 nights of observations at Teide Observatory (23 in 2004 and 4 in 2005). Statistically, most of the turbulence is concentrated close the ground level (2400 m above sea level) with no more than two relative intense turbulent layers at higher altitudes. The temporal evolution of the monthly statistical turbulence profiles indicates that the turbulence is concentrated at low altitude layers in winter.