The title compound, C(20)H(22)BNO(2), is a simple olefinic compound which carries both B and N atoms that are trans to one another. The π-conjugated system of the compound is considered to be isoelectronic with 1,3-butadiene. There are two independent mol-ecules in the asymmetric unit in which the environments around the boron atoms are essentially planar (r.m.s. deviations of 0.0032 and 0.0021 Å for the BO(2)C planes). The dihedral angles of the olefinic planes with the boron planes are 5.70 (11) and 9.74 (9)°, respectively, while the dihedral angles of the olefinic planes with the carbazole planes are 19.37 (3) and 10.74 (6)°. These dihedral angles are consistent with those in 9-ethenylcarbazole and an ethenylboronic ester derivative. The N-Csp(2), B-Csp(2) and C=C bond lengths suggest that the contribution of the canonical structure can be described as N(+)=C-C=B(-).