Hydrogen co-deposition in electroless copper is a cause of embrittlement, voids and blisters. Hydrogen release in the plating bath and its incorporation into the copper films were measured. The amount of hydrogen in the films was determined by monitoring its release over several days at ambient conditions. The mixed potential and the film stress were recorded during film deposition. Adding nickel ions in the plating bath lowers the mixed potential, and it reduces hydrogen incorporation from about 25 at.% to 0.01 at.%. However, the total amount of hydrogen generated per amount of plated copper remains unchanged. For films plated without nickel, the biaxial stress of the films and their hydrogen content are proportional with 3.2 +/- 0.3 MPa/at. % H.