A 4D Variational assimilation system of stratospheric aerosols has been developed. The aerosol assimilation system is applied to the 1.02 μm optical extinction data as measured by SAGE-II (Stratospheric Aerosol and Gas Experiment). A very simple model, a minimal standard aerosol model, was used for both the evolution of aerosols and for the inverse observational operator to map observations into model values. Since this assimilation was set up to provide aerosol analyses for isolated cases, the implementation of a straightforward choice of the first-guess field and corresponding background error covariances is discussed. The results of the aerosol analysis for January 1989 are discussed focussing on the added value of aerosol data assimilation. With a minimal aerosol model, the results show that the assimilation analyses offer the possibility to obtain direct global dynamically consistent information of the 1.02- μm aerosol extinction and aerosol surface area densities. The aerosol analyses can also be used to study dynamical features in greater detail.