The crystal structure of (2Z)-(3,3-dimethyl-3,4-dihydroisoquinolin-1(2Н)-ylidene)nitrosoacetonitrile is determined (T = 150 K, R1 = 0.0435). The compound crystallizes as the E-cis and Z-cis isomers of the nitroso tautomer. Two independent molecules differ in the rotation of the nitroso group about the bond between the dihydroisoquinoline group and the substituent. Analysis of bond lengths reveals their conjugation and prevailing contribution of the zwitter-ionic structures with the positive charge located on the isoquinoline fragment and the negative charge located on the substituent. Molecules having E and Z conformations are connected by the N–HO hydrogen bond (NO 2.922(3) Å) into dimers. The N–H group of the other molecule forms the intramolecular N–HO hydrogen bond (NO 2.544(3) Å) which closes a sixmembered cycle. Electronic absorption spectra are studied, and quantum-chemical modeling of the compound is performed. © 2017, Pleiades Publishing, Inc.