The dimeric condensation product of lactic acid, namely (S,S)-2-[(2-hydroxypropanoyl)oxy]propanoic acid, C(6)H(10)O(5), (I), crystallizes with two independent molecules in the asymmetric unit, which both have an essentially planar backbone. The trimeric condensation product, namely (S,S,S)-3-hydroxybut-3-en-2-yl 2-[(2-hydroxypropanoyl)oxy]propanoate, C(9)H(14)O(7), (II), has one molecule in the asymmetric unit and consists of two essentially planar parts, with the central C-O bond in a gauche conformation. Both molecules of the dimer are involved in intermolecular hydrogen bonds, forming chains with a C(8) graph set. These chains are connected by D(2) hydrogen bonds to form a two-dimensional layer. The trimer forms hydrogen-bonded C(10) and C(2)(2)(6) chains, which together result in a two-dimensional motif. The Hooft method [Hooft, Straver & Spek (2008). J. Appl. Cryst. 41, 96-103] was successfully applied to the determination of the absolute structure of (I).