Tinea infections can be diag- nosed by potassium hydroxide (KOH) examination, which reveals fungal elements when a preparation of scale from a lesion-particularly the active border-is studied under a microscope; culture; and histopathologic examination of a skin biopsy specimen or nail clippings with periodic acid–Schiff stain. Culture may be warranted when a fungal infection is strongly suspected despite a negative KOH result. Unfortunately, dermatophyte cultures can take from 4 to 6 weeks to become positive; therefore, treatment decisions may have to be made before culture findings are reported. A topical antifungal is the initial therapy for tinea cruris, tinea corporis, tinea pedis, and tinea manuum. Tinea capitis, extensive tinea corporis, and tinea unguium are best treated initially with oral antifungal agents, because these infections usually do not respond to topical therapy.