Abstract. In this article we give a classication of the binary, simple, ω−categorical structures with SU−rank 1 and trivial pregeometry. This is done both by showing that they satisfy certain extension properties, but also by noting that they may be approximated by the almost sure theory of some sets of nite structures equipped with a probability measure. This study give results about general almost sure theories, but also considers certain attributes which, if they are almost surely true, generate almost sure theories with very specic properties such as ω−stability or strong minimality.