The analysis of solvent residues trapped into crystals of illicit drugs provides useful evidence for monitoring current use trend in the chemical underground, and is also a suitable tool to achieve the complete chemical characterisation of street drugs for comparative examination of separate specimens. This paper describes a method developed in order to perform simultaneous qualitative and quantitative analysis of solvent residues in cocaine samples. The method is based on GC-MS analysis of solvents after their extraction/concentration from drug matrices accomplished by solid-phase microextraction (SPME) in static head space. The proposed method has been used to detect residues of solvents in 47 illicit street cocaine samples. Quantitative analyses were carried out only for the solvents identified at concentration values higher than 1 ppm. Statistical evaluation of our results allowed us to group the illicit samples into various classes according to different kinds of residual solvent, in connection with different clandestine manufacturing processes used to prepare illicit cocaine.