Nondermatophyte mold (NDM) onychomycosis is difficult to diagnose given that NDMs are common contaminants of the nails and of the mycology laboratory. Diagnostic criteria and definition of cure are inconsistent between studies, which may affect the quality of published data. We identified 6 major criteria used in the literature: identification of the NDM in the nail by microscopy (using potassium hydroxide preparation), isolation in culture, repeated isolation in culture, inoculum counting, failure to isolate a dermatophyte in culture, and histology. Most studies used 3 or more of these (range = 1–5). We recommend using at least 3 of the criteria to rule out contamination; these should include potassium hydroxide preparation for direct microscopy and isolation of the organism in culture. We review geographic distribution and clinical presentations associated with different NDMs. The treatment with the greatest quantity of data and highest reported cure rates is terbinafine, for the treatment of Scopulariopsis brevicaulis and Aspergillus species infections. Topicals such as ciclopirox nail lacquer may also be effective (data originating from Scopulariopsis brevicaulis and Acremonium species infections), especially when combined with chemical or surgical avulsion of the nail. We recommend that future studies use (and clearly indicate) at least 3 of the main criteria for diagnosis, and report the clinical type of onychomycosis and the isolated organism. When evaluating different treatments, we suggest that authors clearly define their efficacy outcomes.