The structure of the free iodine azide molecule was determined by gas-phase electron diffraction. The trans bent geometry determined from the experiment is in agreement with the prediction of MO calculations and with the structure of the rest of the halogen azide series. The following parameters (r(g) bond lengths, Angstrom; r(alpha) angles, degrees) characterize the geometry of the iodine azide molecule : (N-N)(mean) 1.204 +/- 0.004, Delta(NN) 0.113 +/- 0.022, I-N 2.120 +/- 0.010, N-N-N 169.6 +/- 3.0, and I-N-N 106.6 +/- 1.1.