Abstract The molecular structures of 2-chloropropene and 2-bromopropene have been determined at 20°C by combined analysis of electron diffraction and microwave spectroscopic data. The following results, expressed in terms of r g distances and r α angles, were obtained for 2-chloropropene: r (CC) = 1.338(3) A, r (CC) = 1.495(4) A, r (CCl) = 1.744(2) A, r (=CH) avg = 1.089(8) A, Δ r (CH) = 0.008(10) A, ∠CCC = 126.3(2)°, ∠CCCl = 119.0(3)°, ∠CCH( trans to Cl) = 118.7(2.0)°, ∠CCH( cis to Cl) = 125.0(2.0)°, ∠CCH(in plane) = 112.1(2.3)°, ∠CCH(out of plane) = 110.6(1.7)°. The results obtained for 2-bromopropene were: r (CC) = 1.343(4) A, r (CC) = 1.496(5) A, r (CBr) = 1.909(3) A, r (CH) avg = 1.113(9) A, ∠CCC = 126.9(3)°, ∠CCBr = 118.3(5)°, ∠CCH avg = 103.8(2.1)°. For 2-bromopropene a second least-squares minimum was found for a model having ∠CCBr = 123.5(7)°. This model could not be rejected on a statistical basis. Quoted uncertainties in geometrical parameters are 3σ.