The title compound, bis(borato)dodeca(tert-butoxo)octadecalithium, [Li(18)(BO(3))(2)(C(4)H(9)O)(12)], is formulated conveniently as [(((t)BuOLi)(3)(Li(3)BO(3)))(2)((t)BuOLi)(6)]. A central 12-membered ring and two outer six-membered rings are formed by alternating Li(+) cations and alkoxide O atoms. Sandwiched between the central ring and each of the outer rings is a planar array of three further Li(+) cations surrounding a [BO(3)](3-) anion. Thus, the molecule consists of a cationic [Li(18)(O(t)Bu)(12)](6+) cage encapsulating two borate anions. This compound is the first example of a structurally characterized polynuclear lithium borate, and a rare case of a lithium alkoxide cage with nuclearity greater than eight. All the alkoxide ligands are triply bridging, and the lithium ions have trigonal-planar, trigonal-pyramidal and fourfold coordination, all with major distortions from regular coordination geometry.