We present a case of brilliant green staining of the fingernails caused by the patient's use of an antiseptic dye to self-treat onychodystrophy. Brilliant green is an antiseptic dye used since at least the early 20th century for the treatment of bacterial infections. It was originally used for wound care and as an anti-inflammatory medication; however, its use for both of these indications is limited. Because of its ease of use, low cost, and accessibility, brilliant green has been promoted for use in resource-poor settings and as an anticancer therapy. Dermatologists should be aware of brilliant green, as well as its indications, common uses, and adverse effects, and should be able to differentiate it from other causes of green nails.