Scopulariopsis brevicaulis was demonstrated in 226 out of 5,600 patients examined for abnormal toe-nails. Among 3,700 patients without onychomycosis S. brevicaulis was demonstrated as a contaminant in 2%. Onychomycosis, present in 1,925 patients, was caused by S. brevicaulis in 6%, but 10% of these cases were mixed infections with dermatophytes. In the approximately 1,800 cases of onychomycosis due to other reasons, S. brevicaulis was a contaminant in 2%. A specific finding of S. brevicaulis on direct microscopy is diagnostic, and a number of colonies ≥ 10 supports the diagnosis, while in the presence of ≤ 3 colonies and no S. brevicaulis on direct microscopy the diagnosis is unlikely. Onychomycosis due to S. brevicaulis was most often diagnosed in elderly persons, with equal frequency in men and wo