A hydrocracking process for treating a first and a second heavy hydrocarbon feedstream, in which the first heavy hydrocarbon feedstream contains undesired nitrogen-containing compounds, sulfur-containing compounds and poly-nuclear aromatic compounds. The process includes contacting the first heavy hydrocarbon feedstream with adsorbent material to produce a hydrocarbon stream having a reduced content of nitrogen-containing, sulfur-containing compounds and poly-nuclear aromatic compounds. The second heavy hydrocarbon feedstream is combined with the adsorbent-treated heavy hydrocarbon stream. The combined stream is charged to a hydrocracking reaction unit. The hydrocracked effluent is fractioned to recover hydrocracked products and a bottoms stream containing heavy poly-nuclear aromatic compounds, and bottoms are contacted with adsorbent material to produce an adsorbent-treated fractionator bottoms stream having a reduced content of heavy poly-nuclear aromatic compounds, and are recycled to the hydrocracking reaction unit.