A polymer is composed of recurring units of hydroxyvinylnaphthalene, (meth)acrylic units having a lactone ring fused to a bridged ring, and (meth)acrylic units having acid labile groups. A positive resist composition comprising the polymer as a base resin, when exposed to high-energy radiation and developed, exhibits a high sensitivity, a high resolution, and a minimal line edge roughness due to controlled swell during development.