The structure of the title uric acid derivative, C(7)H(8)N(4)O(5), from human kidney stones, is characterized by the C and O atoms of one of the two hy-droxy-methyl groups being disordered nearly equally over three different sites. In the crystal, mol-ecules are connected by a three-dimensional hydrogen-bonding scheme though they look stacked in planes nearly parallel to ([Formula: see text]04).