The gas-phase stability of bridgehead carbocations has been determined by Fourier transform ion cyclotron resonance spectroscopy (FT ICR) based on dissociative proton attachment (DPA) of bridgehead bromides, chlorides, and alcohols. When appropriate leaving group corrections are applied, the relative ion stabilities obtained from these precursors are identical. The relative rate constants (log k) for solvolysis of bridgehead derivatives correlate with the stabilities of the cations over the entire reactivity range. Theoretical calculations of the stabilities of the ions relative to those of the respective hydrocarbons at the MP2/6-311G** level agree fully with the experimental data.