Solvent-induced crystallization (SINC) was observed in a polyetherimide (PEI), a thermoplastic used as a matrix in carbon fiber composites. This observation was made using wide angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and optical microscopy. It was discovered that methylene chloride induces crystallization in the PEI by penetrating the surface and swelling the bulk polymer. Prepreg processed using N-methyl pyrrolidone (NMP) was also crystalline. One processed above the crystalline melting point (Tm), no crystallinity in the sample was found, as the PEI did not crystallize from the melt. The observed crystallization of both the neat polymer and its carbon fiber prepreg was exclusively through a solvent-induced process, although it is likely that the mechanism through which crystallization occurs during solvent prepreg processing is different than the diffusion-controlled mechanism demonstrated with methylene chloride. A solvent prepregging process may involve a low molecular weight or monomer solution as well as other polymerization by products. Measurements using WAXS showed a maximum degree of crystallinity of 30%, as induced by methylene chloride. A value of 85 J/g for the heat of solvent-induced crystallization in the PEI was calculated from the DSC measurements.