An improved synthesis of a compound of potential astrochemical interest, allenylisocyanide (H2C=C=CHNC), is reported together with its microwave spectrum, which has been investigated in the 8-120 GHz spectral range to facilitate a potential identification in interstellar space. The spectra of the ground vibrational state and of five vibrationally excited states belonging to three different vibrational modes have been assigned for the parent species. A total of 658 transitions with a maximum value of J = 71 were assigned for the ground state and accurate values obtained for the rotational and quartic centrifugal distortion constants. The spectra of five heavy-atom (C-13 and N-15) isotopologues were also assigned. The dipole moment was determined to be mu(a) = 11.93(16) x 10(-30) C m, mu(b) = 4.393(44) x 10(-30) Cm, and mu(tot) = 12.71(16) x 10(-30) C m. The spectroscopic work has been augmented by theoretical calculations at the CCSD/cc-pVTZ and B3LYP/cc-pVTZ levels of theory. The theoretical calculations are generally in good agreement with the experimental results.