A hydroconversion catalyst composition includes a catalytically active matrix having a surface area of between about 50 m.sup.2 /g to about 290 m.sup.2 /g, a silicious molecular sieve support medium distributed through the matrix and having a surface area of between about 250 m.sup.2 /g to about 1200 m.sup.2 /g and a catalytically active phase supported on the support medium and including a first metal selected from group IIIA of the periodic table of elements and a second metal selected from group VIB of the periodic table of elements. The matrix preferably further includes aluminum, gallium, cobalt, molybdenum, and phosphorus.