A resist composition which is stable relative to solvents used in immersion lithography processes and displays excellent sensitivity and resist pattern profile, and a method of forming a resist pattern that uses such a resist composition are provided. The resist composition is in accordance with predetermined parameters, or is a positive resist composition comprising a resin component (A) which contains an acid dissociable, dissolution inhibiting group and displays increased alkali solubility under the action of acid, an acid generator component (B), and an organic solvent (C), wherein the component (A) contains a structural unit (a1) derived from a (meth)acrylate ester containing an acid dissociable, dissolution inhibiting group, but contains no structural units (a0), including structural units (a0-1) containing an anhydride of a dicarboxylic acid and structural units (a0-2) containing a phenolic hydroxyl group.