The present invention is directed to a process for the catalytic hydrogenation of a starting material containing 4,4′-diamino-diphenylmethane (4,4′-MDA) or its mixtures with 2,4′-diamino-diphenylmethane, 2,2′-diamino-diphenylmethane and/or higher ring compounds of the diphenylmethane series to a hydrogenation product having a trans-trans isomer content of 4,4′-diamino-dicyclohexylmethane (4,4′-HMDA) of about 15 to 40 weight percent, based on the diamine content of the hydrogenated product, by continuously hydrogenating in at least one fixed bed reactor at a temperature of about 100 to 190°C and a pressure of about 50 to 350 bar in the presence of a ruthenium catalyst on a catalyst support having a BET surface area of about 70 to 280 m²/g and an average pore diameter d p of about 10 to 320 Å, the catalyst being prepared by impregnating the catalyst support to a penetration depth of at least about 50 µm with a soluble ruthenium compound in an amount sufficient to provide a catalyst containing about 0.1 to 5 weight percent ruthenium and subsequently reducing the soluble ruthenium compound to ruthenium.