Fusaproliferin is a toxic sesterterpene isolated from Fusarium proliferatum, a widespread pathogen of cereals. Its absolute configuration has been determined by single crystal X-ray diffraction analysis. Fusaproliferin is considered to be a sesterterpene with a new ring skeleton having four C=C double bonds and four chiral atoms. The configurations of the four chiral atoms C10, C14, C15, and C19 are (R), (S), (R), and (S), respectively. In the solid state the macrolide Shows a concave hydrophobic surface and hydrophilic convex face. The absolute configuration of C14 and C15 is the same as that observed for retigeranic acid, consistent with fusaproliferin being formed via a sesterterpenic-type biosynthetic pathway.