X-ray powder diffraction data, unit-cell parameters, and space group for a sodium azobarbituric acid dihydrate are presented [a = 3.546 (1) Å, b = 9.210 (2) Å, c = 9.738 (4) Å, α = 104.07 (4)°, β = 98.09 (6)°, γ = 98.80 (2)°, unit-cell volume V = 299.6 Å3, Z = 1, and space group P − 1]. All the measured lines were indexed. No detectable impurities were observed.