The photodissociation of homogeneous methyl nitrite clusters, [CH3ONO](n) with n approximate to 400-1000, was investigated in a supersonic jet using excitation mainly at 365 nm, which corresponds to S-0-S-1 (n pi*) excitation in the monomer. Besides the two types of NO(<(X)over bar (II)-I-2) photofragment distributions, a rotationally relaxed one (T-rot similar to 250 K) and a nonthermally "hot" one ([J "]=35.5) which result from the primary dissociation step CH3ONO-->CH3O+NO of cluster-bound CH3ONO, we observed the products HNO(<(X)over tilde (1)A’>) and H2CO(<(X)over tilde (1)A(1)>) by state-selected LIF spectroscopy. Their product-yield excitation spectra and their formation dependence on the backing pressure revealed that HNO and H2CO originate exclusively from cluster photodissociation and not from primary photodissociation of the monomer. The mechanism of their formation was found to be the disproportionation reaction of the primary photofragments, CH3O+NO-->HNO+H2CO, mediated by caging of the cluster environment. The fragments collide with, and recoil at, the solvent shell, followed by subsequent recombination, disproportionation, or escape from the evaporating solvent cage. The present results are consistent with previous findings on the photolysis of isolated CH3ONO molecules in solid noble gas matrices where exclusively the products HNO and H2CO were found.