During Leg 66 eight sites were drilled to form a transect across the Middle America Trench off southwestern Mexico. Cores from these sites show that accretion began approximately 10 MY ago and has continued to the present. Accretion began with offscraping followed by a 2- to 4- MY episode of folding and faulting with uplift rates of 400-500 m/MY; uplift then slowed to 100-200 m/MY, and seismically resolved deformation ceased as the wedge appeared to rise evenly. Approximately 33% of the sediment flux input into the subduction zone, mainly trench sand and slump deposits, is scraped off and incorporated into the toe of the lower slope; an additional 33% is initially subducted but then peeled off to underplate the accretionary wedge; the remaining 33% is subducted landward beneath the overhanging lip of continental crust. Although we find no direct evidence of tectonic erosion, the large amount of sediment subducted makes tectonic erosion feasible.