We report the results of a low-pressure (ICR) and high-pressure (SIFT) investigation of the ion-molecule reactions of C3H3+. Two isomeric forms of C3H3+ are present : HCCCH2+ and c-C3H3+. Rate coefficients and product ratios are reported for each technique for a variety of neutral reactants including H-2, NH3, C2H2, CH3OH, and CH3CN. Most reactions occur via a long-lived association complex. Large differences in reactivity and differences in product distributions between the two techniques are rationalized in terms of the association complex lifetime.