A stable, non-peptide inhibitor of the protease from type 1 human immunodeficiency virus has been developed, and the stereochemistry of binding defined through crystallographic three-dimensional structure determination. The initial compound, haloperidol, was discovered through computational screening of the Cambridge Structural Database using a shape complementarity algorithm. The subsequent modification is a non-peptidic lateral lead, which belongs to a family of compounds with well characterized pharmacological properties. This thioketal derivative of haloperidol and a halide counterion are bound within the enzyme active site in a mode distinct from the observed for peptide-based inhibitors. A variant of the protease cocrystallized with this inhibitor shows binding in the manner predicted during the initial computer-based search. The structures provide the context for subsequent synthetic modifications of the inhibitor.