We report on three cases of tinea capitis (black-dot ringworm, BDR) in a Japanese high-school wrestling team caused by Trichophyton (T.) tonsurans. Case 1: A 17-year-old male wrestler, who was diagnosed as having tinea corporis effecting the right ear, trunk and thighs, was treated with griseofulvin in August 2001. In February, 2002, he visited our clinic again because of recurrence of the tinea on the nape. Asymptomatic black dots were found on his scalp. Direct KOH examination of the black dots revealed abundant arthroconidia entirely contained within, and filling, the hair shafts. Tinea capitis (BDR) was diagnosed and oral griseofulvin was prescribed again. Case 2: A 16-year-old male wrestler, a team mate of the patient in Case 1, visited our clinic in April 2002 suffering from pruritic erythema on the right side of the scalp. Several black dots were observed on the erythema. Direct KOH examination of the black dot indicated tinea capitis (BDR). Case 3: We visited the patients' school and screened all 11 members of the team for dermatophytosis. Another 17-year-old male wrestler was found to have BDR. In all three cases, BDR was caused by T. tonsurans and treatement with oral griseofulvin was succesful. Tinea capitis (BDR), caused by T. tonsurans, may be a major source of fungi involved in the epidemic of the dermatophytosis. Therefore, accurate diagnosis of, and adequate treatment for, tinea capitis is essential.