N,N'-diphenyl-N,N'-diethylurea (C(17)H(20)N(2)O) crystallizes in the space group P2(1)/c. The unit cell constants are: a = 10.42 +/- 0.01 A, b = 16.86 +/- 0.02 A, c = 10.66 +/- 0.001 A, beta = 125 degrees 16' +/- 5'; Z = 4, D(x) = 1.16 g.cm(-3), D(meas) = 1.16 +/- 0.01 g.cm(-3). Data for 1392 reflections were collected at room temperature on a Picker automated diffractometer. The crystal structure was solved by direct methods and refined by bloc-diagonalized matrix least-squares calculations. The molecule is characterized by a pseudo C(2) symmetry; both phenyl groups are trans with respect to the oxygen atom. The hybridization of the two nitrogen atoms is intermediate between trigonal and tetrahedral; the nonplanar distortion of the amide groups is about 30 degrees . The amide C-N bond lengths are 1.37 A.