BACKGROUND: The last 10 years have seen a substantial increase in the number of studies reporting the efficacy of the various antifungal agents used to treat onychomycosis. AIM: To examine the definitions of efficacy parameters reported in clinical studies on the treatment of onychomycosis and discuss the importance of standardized reporting. METHODS: We searched MEDLINE (1966-2001) for studies in which oral treatments, griseofulvin, ketoconazole, terbinafine (continuous and pulse), itraconazole (continuous and pulse), and fluconazole, were used to treat dermatophyte onychomycosis. RESULTS: Mycologic cure was predominantly defined as negative microscopy and culture. Unlike mycologic cure, clinical parameters (e.g. clinical response, clinical cure) were variably defined. Subjective terms, such as "cure" or "markedly improved," were used; although these terms appear to be explicit, what is considered to be "cured" or "markedly improved" by one evaluator may not be by another. Also, infected nails were clinically evaluated to determine the response to treatment. Studies measured the distance between the proximal nail fold and a notch in the nail plate, at the junction between the diseased and normal-appearing nail, or in some cases estimated the diseased nail plate involvement. CONCLUSIONS: This review of the literature on systemic agents used to treat onychomycosis shows that standard and explicit definitions are required for the accurate comparison of the effectiveness of the various therapies.