Evolutionary relationships among twenty isolates of the deuteromycete mycorrhizal fungus Cenococcum geophilum were examined using molecular techniques. The ribosomal RNA region containing internal transcribed spacers (ITS1 and ITS2) and the 5.8 S gene were amplified using the polymerase chain reaction (PCR). The PCR products were analyzed with restriction site mapping (20 isolates) and DNA sequencing (18 isolates). Maximum parsimony, UPGMA (unweighted pair-group method with arithmetic mean) and maximum likelihood methods were utilized in phylogenetic analyses.