This paper presents particle size distributions of stratospheric aerosols derived from solar occultation data measured by the instrument ORA (an acronym for Occultation RAdiometer) during the period August 1992-May 1993. Starting from the UV-visible wavelength dependence of extinction coefficient profiles, an algorithm is developed that allows to retrieve the three parameters of an equivalent log-normal distribution and that makes use of vertical regularization. Comparison of retrieved mode radius and particle number density with existing data is found to be satisfactory. The evolution of the stratospheric aerosols is clearly influenced by sedimentation and coagulation as expected but also by vertical circulation. In a simple 1-D model, we derive the vertical wind profile and we interpret the temporal evolution of the particle mode radius.