The microwave spectra of benzyl cyanide, C6H5CH2CN, were recorded using a molecular jet Fourier transform microwave spectrometer operating in the frequency range 2–26.5 GHz. Analyses of the 14N quadrupole hyperfine structures were performed simultaneously with the rotational frequencies. Rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants χaa and χbb − χcc were all determined with very high accuracy in a fit containing 465 lines with standard deviation within the measurement accuracy. Results from quantum chemical calculations at many levels of theory employing the MP2 method indicate a non-planar heavy atom skeleton structure, where the CH2CN group is tilted up to 50° with respect to the phenyl ring. This conflicts with results from many calculations employing density functional theory methods and also with the conclusion of a previous microwave spectroscopic work (X.-Z. Liu, R.K. Bohn, S.A. Sorenson, N.S. True, J. Mol. Struct. 243 (1991) 325–339), stating that the CH2CN group and the phenyl ring are in-plane. By comparing the planar defect with those of several planar molecules reported in the literature, and with extensive support from quantum chemistry, we present for the first time evidence suggesting that the heavy atom structure of benzyl cyanide is probably not planar.