1,3-Diethyl-2-thio-barbituric acid reacts with 2,5-dimethoxy-benzaldehyde to form the title Knoevenagel product, C(19)H(22)N(2)O(4)S. In the compound, the two six-membered rings at either end of the three-membered -CHCHCH- chain are nearly coplanar with this fragment (r.m.s. deviation of the two six-membered rings and the three chain atoms = 0.08 Å).