The use of griseofulvin, orally administered, in patients with onychomycosis, has been the subject of many reports. It is well known that, clinically, it is sometimes difficult to distinguish onychomycosis from psoriasis of the nails, for which reason we have attempted a clinical trial of griseofulvin in some special cases of both diseases, and compared their course. Methods The drug was given in the usual doses described in other reports. The usual toxicity studies, including sperm counts, were also done. From 262 patients treated with griseofulvin, three different types were selected: (1) sixty-seven patients with mycotic nail involvement; (2) eleven patients with cutaneous and scalp psoriasis, as well as nail involvement; (3) two patients with simultaneous involvement of nails with psoriasis and fungus infection. Observations In order to compare the course of psoriasis unguium with that of trichophytosis of the nails, 11 patients with fungus disease were selected at random.