A low-temperature structure of ginkgolide A monohydrate, (1R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)-3-(1,1-dimethylethyl)-hexa­hydro-4,7b-di­hydroxy-8-methyl-9H-1,7a-epoxymethano-1H,6aH-cyclo­penta­[c]­furo­[2,3-b]­furo­[3′,2′:3,4]­cyclopenta­[1,2-d]­furan-5,9,12(4H)-trione monohydrate, C₂₀H₂₄O₉·H₂O, obtained from Mo Kα data, is a factor of three more precise than the previous room-temperature determination. A refinement of the ginkgolide A monohydrate structure with Cu Kα data has allowed the assignment of the absolute configuration of the series of compounds. Ginkgolide C sesquihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11S,11aR)-3-(1,1-di­methyl­ethyl)-hexa­hydro-2,4,7b,11-tetrahydroxy-8-methyl-9H-1,7a-epoxy­methano-1H,6aH-cyclopenta­[c]­furo­[2,3-b]­furo­[3′,2′:3,4]­cyclo­penta­[1,2-d]­furan-5,9,12(4H)-trione sesquihydrate, C₂₀H₂₄O₁₁·1.5H₂O, has two independent diterpene mol­ecules, both of which exhibit intramolecular hydrogen bonding between OH groups. Ginkgolide J dihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)-3-(1,1-di­methyl­ethyl)-hexa­hydro-2,4,7b-tri­hydroxy-8-methyl-9H-1,7a-epoxy­methano-1H,6aH-cyclo­penta­[c]­furo­[2,3-b]furo[3′,2′:3,4]­cyclo­penta­[1,2-d]­furan-5,9,12(4H)-trione dihydrate, C₂₀H₂₄O₁₀·2H₂O, has the same basic skeleton as the other ginkgolides, with its three OH groups having the same configurations as those in ginkgolide C. The conformations of the six five-membered rings are quite similar across ­ginkgolides A–C and J, except for the A and F rings of ginkgolide A.