Asymmetric synthesis of amphidinolide Q, a cytotoxic macrolide from the cultured dinoflagellate Amphidinium sp., has been accomplished with Julia coupling, Myers alkylation, and Yamaguchi lactonization. The absolute configuration of amphidinolide Q was confirmed to be 1 from comparison of the NMR data and [α]D values of synthetic and natural amphidinolide Q.