The title co-crystal [systematic name: 3-(1,3-dioxoisoindolin-2-yl)propanoic acid-1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione (1/1)], C(8)H(10)N(4)O(2)·C(11)H(9)NO(4), is the combination of 1:1 adduct of N-phthaloyl-β-alanine with caffeine. The phthalimide and purine rings in the N-phthaloyl-β-alanine and caffeine mol-ecules are essentially planar, with r.m.s. deviations of the fitted atoms of 0.0078 and 0.0118 Å, respectively. In the crystal, the two mol-ecules are linked via an O-H⋯N hydrogen bond involving the intact carb-oxy-lic acid (COOH) group. The crystal structure is consolidated by C-H⋯O inter-actions. The H atoms of a methyl group of the caffeine mol-ecule are disordered over two sets of sites of equal occupancy.