Dimerization of styrene has been carried out in the presence of acid large-pore zeolites with Y and beta structure. Besides trimers and oligomers, variable amounts of the three known dimers are also formed depending on the different level of Na+-to-H+ exchange. framework Si/Al ratio and crystal size. The average activity per acid site of zeolites is lower than that measured for H2SO4. This fact is not likely due to the acid strength demands of the dimerization, but more probably to diffusion limitations of the organic compounds through the zeolite micropores. Finally, depending on the acidity of the zeolite, a consecutive cyclization of the open dimer to the indane dimers, which are formed with a significant degree of diastereoselectivity, was observed.