A process for the preparation of 3,3,5-trimethylcyclohexanone by catalytic hydrogenation of isophorone, wherein the hydrogenation is carried out in a plurality of two or more series-connected loops, wherein each loop involves the use of one reactor, which comprises: (a) feeding isophorone and hydrogen to an upper part of a reactor to catalytically hydrogenate said isophorone to produce a hydrogenation product, (b) recycling a portion of said hydrogenation product back into said upper part of said reactor, (c) feeding the remainder of said hydrogenation product from said reactor to an upper part of a subsequent reactor wherein isophorone is catalytically hydrogenated to produce a subsequent hydrogenation product, and wherein a portion of said subsequent hydrogenation product has been recycled and is fed with said remainder of said hydrogenation product to said upper part of said subsequent reactor, (d) repeating step (c) until the subsequent reactor is the last reactor, (e) recovering the remainder of said subsequent hydrogenation product from said last reactor, and (f) obtaining 3,3,5-trimethylcyclohexanone from the product of step (e).