The crystal structures of the natural and recombinant antiviral lectin scytovirin (SVN) were solved by single-wavelength anomalous scattering and refined with data extending to 1.3 Å and 1.0 Å resolution, respectively. A molecule of SVN consists of a single chain 95 amino acids long, with an almost perfect sequence repeat that creates two very similar domains (RMS deviation 0.25 Å for 40 pairs of Cα atoms). The crystal structure differs significantly from a previously published NMR structure of the same protein, with the RMS deviations calculated separately for the N- and C-terminal domains of 5.3 Å and 3.7 Å, respectively, and a very different relationship between the two domains. In addition, the disulfide bonding pattern of the crystal structures differs from that described in the previously published mass spectrometry and NMR studies.