Treatment of onychomycosis is a difficult task which requires deep knowledge about these mycoses, the interpretation of mycologic studies results, the antifungal drugs used, their side effects and their interactions with other treatments. For these reasons they have been considered as very difficult to treat and their treatments as being very long and toxic. These considerations are not completely truthful. Several aspects of medical interest about these fungal infections, including their etiologic agents, risk factors that increase their prevalence, pathogenesis, the most important clinical data to be taken into account before prescribing treatments and their efficacy, side effects and drug interactions of the different antifungal medications used in onychomycosis are presented in this review. The aim of it is to serve as a guide for clinicians and dermatologists in the study and treatment of onychomycosis. The combined treatments, which have improved the clinical and mycological results of medication in these fungal infections, are also revised. Finally we recognized that, although onychomycosis are not impossible to treat, except a few cases, the available treatments are not ideal, so this subject is open for new clinical and pharmacologic research.