SETTER web-server utilizes SETTER (SEcondary sTructure-based TERtiary Structure Similarity Algorithm) method for fast and accurate structural pairwise alignment. The server is capable of comparing a pair of RNA structures or using one strucutre as a query and search against a user-defined database of RNA structures. The efficiency of the algorithm is given by the decomposition of the RNA structure into the set of non-overlapping generalized secondary structure motifs (GSSUs). GSSU usually resembles a hairpin motif possibly containing bulges and/or internal loops in its stem part. A segmentation to GSSUs offers good scalability with respect to the structure size (SETTER scales linearly with the structure size) because the number of residues in GSSUs (SETTER scales quadratically with the GSSU size) generally does not increase with increased size of the RNA structure. The underlying SETTER algorithm is both accurate and very fast, and does not impose limits on the size of aligned RNA structures. SETTER is able to compare a pair of even the largest RNA structure in less than one minute.