A total of 1,101 patients was studied for the incidence and distribution of dermatophytes in the San Francisco Bay Area from 1974 to 1978. 267 dermatophytes were isolated and identified. Trichophyton rubrum and Triehophyton tonsurans were the most prevalent dermatophytes. T. rubrum caused 83% of tinea pedis, 82% of tinea unguium, 80% of tinea manuum and 66% of tinea cruris. T. tonsurans was the major cause of tinea capitis (60%) followed by Microsporum canis. Microsporum audouinii was not encountered in this survey.