We report three cases involving 7- to 8-year-old children from a Swiss school who had refractory tinea capitis due to an unusual strain of Microsporum audouinii which perforates hair in vitro. The patients showed no response to modern oral antifungal drugs like terbinafine and fluconazole. After switching to oral griseofulvin, two of the patients had a complete recovery, while the third was cured after the introduction of oral itraconazole. Given the high potential for contagion of this anthropophilic dermatophyte, all family members and three entire school classes were screened using the 'toothbrush technique'. Three family members and five class-mates were found to be asymptomatic carriers of M. audouinii and were consequently treated to avoid further transmission or reinfection of the treated patients. This is the first report of an outbreak of M. audouinii in Switzerland and underlines the importance of screening all contacts of patients with M. audouinii tinea capitis. Further, the effectiveness of griseofulvin in Microsporum tinea capitis has been corroborated, while newer antimycotic drugs like fluconazole or terbinafine failed.