The crystal structure of cafetite, ideally Ca[Ti₂O₅](H₂O), (monoclinic, P2₁ln, a = 4.9436(15), b = 12.109(4), c = 15.911(5) Å, β = 98.937(5)°, V = 940.9(5) ų, Z = 8) has been solved by direct methods and refined to R₁ = 0.057 using X-ray diffraction data collected from a crystal pseudo-merohedrally twinned on (001). There are four symmetrically independent Ti cations; each is octahedrally coordinated by six O atoms. The coordination polyhedra around the Ti cations are strongly distorted with individual Ti-O bond lengths ranging from 1.743 to 2.223 Å (the average <Ti-O> bond length is 1.98 Å). Two symmetrically independent Ca cations are coordinated by six and eight anions for Ca1 and Ca2, respectively. The structure is based on [Ti₂O₅] sheets of TiO₆ octahedra parallel to (001). The Ca atoms and H₂O groups are located between the sheets and link them into a three-dimensional structure. The structural formula of cafetite confirmed by electron microprobe analysis is Ca[Ti₂O₅](H₂O), in contrast to the formula (Ca,Mg)(Fe,Al)₂Ti₄O₁₂4H₂O suggested by Kukharenko et al. (1959). The wrong chemical formula suggested for cafetite by Kukharenko et al. (1959) is probably due to admixtures of magnetite or titanomagnetite in their samples. Cafetite is chemically related to kassite, CaTi₂O₄(OH)₂, but differs from it in structure and structural formula.