This account describes our endeavors on the total synthesis and structure elucidation of a marine macrolide glycoside, (−)-lyngbyaloside B. This natural product was isolated as a moderately cytotoxic constituent from the Palauan cyanobacterium Lyngbya sp. Our investigation started with the total synthesis of a nonnatural analog, (−)-13-demethyllyngbyaloside B, which was completed by exploiting an esterification/ring-closing metathesis strategy for the construction of the macrocyclic framework. Our efforts toward (−)-lyngbyaloside B were frustrated by the difficulties associated with the construction of the macrocycle involving an acylated tertiary alcohol. Eventually, the first total synthesis of the proposed structure of (−)-lyngbyaloside B was completed via an acyl ketene macrocyclization to forge the macrocyclic backbone. Because the proposed structure turned out to be erroneously assigned, we deduced the correct structure of (−)-lyngbyaloside B on the basis of the NMR data of the authentic material and molecular modeling. Ultimately, our revised structure was unambiguously verified through total synthesis.