BACKGROUND: Dermatophytes are usually identified on the basis of macroscopic characteristics and microscopic examination of the cultures. Identification of dermatophytes often remains difficult or uncertain because there are variations from one isolate to another and overlapping characteristics between species. OBJECTIVE: To identify dermatophyte species producing numerous microconidia and resembling Trichophyton mentagrophytes by DNA sequence analysis. METHODS: The complete ITS1 + 5.6s + ITS2 rDNA region of various dermatophytes isolated in culture was amplified by PCR and sequenced. RESULTS: Nine isolates of a fast-growing dermatophyte species were identified as Arthroderma benhamiae by DNA sequencing. Retrospective investigations revealed that the isolates were from 8 children and 1 adult suffering from inflammatory dermatophytosis. Eight of the 9 patients had had previous contact with rodents, mostly guinea pigs. CONCLUSION: It is the first time that A. benhamiae is reported in Switzerland. In cases of dermatophytosis attributed to A. benhamiae, a rodent is the most likely cause of infection.