Triphenylmethylcyclopentadiene exists as a mixture of isomers, the minor and major components of which are shown to be 1-triphenylmethylcyclopentadiene (1) and 2-triphenylmethyl-cyclopentadiene (2), respectively.Direct irradiation of a mixture of1and2led to formation of 5,6,6,-triphenylbicyclo[3.1.0]hex-2-ene (3) via rearrangement of1. Acetophenone-sensitized irradiation of the same mixture gave3as well as a two component mixture of photodimers of1and/or2. Results are interpreted in terms of the di-π-methane rearrangement mechanism.