Background: Onychocola canadensis is a nondermatophyte mold associated with onychomycosis particularly in temperate climates (eg, Canada, New Zealand, and France). The slow growth rate of O canadensis and lack of resemblance to any other known nail-infecting fungus may have delayed its discovery. We are aware of 23 mycologically confirmed cases of O canadensis in the literature. Objective: We describe 10 previously unreported Canadian patients, specimens from whom grew O canadensis . We also review the literature on infections associated with this organism. Methods: Cases of O canadensis onychomycosis were diagnosed on the basis of (1) the finding of compatible filaments on direct microscopy of nail and (2) consistent culture from repeated specimens. All patients from whom O canadensis was isolated were followed up, but those in whom outgrowth was not consistent were not accepted as having “authentic” infections. Results: In 10 patients O canadensis was found to be associated with distal lateral subungual onychomycosis (6 patients), white superficial onychomycosis (1 patient), and as an insignificant contaminant in the nails of 3 patients. Less commonly the organism may cause tinea manuum or tinea pedis interdigitalis. O canadensis appears to be more frequent in the elderly, especially females. It is not unusual for a patient with onychomycosis caused by O canadensis to be a gardener or farmer, suggesting that the infectious inoculum may originate from the soil. The optimal therapy for onychomycosis caused by this organism remains unclear. Conclusion: O canadensis may be the etiologic agent of distal and lateral subungual or white superficial onychomycosis; however, it may sometimes be present in an abnormal-appearing nail as an insignificant finding, not acting as a pathogen. (J Am Acad Dermatol 1998;39:410-7.)