Microsporum canis is the causative organism in less than 10% of all tinea capitis infections in the UK. Transmission is generally via contact with an infected family pet and there are only rare reports of case clustering. This article describes an outbreak of M. canis in a primary school classroom demonstrating human-to-human spread from an index case who was presumed to have acquired the infection prior to arriving in the UK. There was no suggestion of clinical improvement following 4 weeks of oral terbinafine 125 mg daily and treatment was changed to griseofulvin. The Health Protection team screened class members and confirmed cases (either clinically or mycologically) were also treated with griseofulvin 10-20 mg/kg/day for 10 weeks. Classmates and siblings of classmates were recommended to use selenium sulphide or ketoconazole-containing shampoo twice weekly.