The title compound, 2C(17)H(20)N(2)O·CH(2)Cl(2), was obtained by N-oxidation of the parent formamidine with m-chloro-peroxy-benzoic acid (m-CPBA). This is the first use of the above-mentioned synthetic route for the preparation of hydroxy-amidines. The title compound crystallizes as a cyclic dimer resulting from the presence of O-H⋯O and N-H⋯N hydrogen bonds.