A survey of dermatophytes, isolated from human patients seeking medical attention, was conducted for the years 1993 to 1995. Data were collected from 23 states throughout the continental United States and the District of Columbia and from 44 to 45 laboratories. These data were compared with the results of two earlier surveys (1979 to 1981 and 1985 to 1987). In contrast to the earlier surveys Trichophyton tonsurans became the most frequently isolated dermatophyte (44.9%) followed by T. rubrum (41.3%), T. mentagrophytes (8.5%), Microsporum canis (3.3%) and Epidermophyton floccosum (1.1%). Other dermatophytes were recovered from less than 1%. The increase in T. tonsurans from 27.9% in the 1979 to 1981 survey, to 41.3% in the current survey, accompanied by the decline of T. rubrum from 53.7% to 41.3% is statistically significant (P < .001.) (J Am Acad Dermatol 1998;39:255-61.)