Background: Myxoid cysts located beneath the nail are very different from those within the nailfold and there is no established literature on their diagnosis and therapy. Objective: Thirty-five cases of subungual myxoid cyst are described in which the diagnosis was confirmed by magnetic resonance imaging, surgical exploration, or both. Methods: The clinical characteristics of all cases of subungual myxoid cysts confirmed in 3 specialist nail clinics are reported. Twenty cases were confirmed by magnetic resonance imaging. Histologic details were recorded in 4 cases. Results: Thirty-four patients (22 female, 12 male) presented with a subungual tumor of the thumb (n = 25) or finger (n = 10). The 3 main clinical variables were color of the lunula, transverse nail curvature, and integrity of the nail. In 26 cases the lunula was discolored; it was red in 22 cases, blue in 3, and as part of a longitudinal leukonychia in one. Transverse curvature was increased in 29 cases and was normal in 5 cases; in one case the nail was destroyed. In 11 cases, the change in curvature led to lateral ingrowing. Surgery (n = 22), sclerosant (n = 1), and spontaneous discharge (n = 2) all resulted in resolution. Ten patients had no treatment. Conclusion: This study describes 35 subungual myxoid cysts having characteristic features that allow clinical diagnosis. They respond to a range of treatments. (J Am Acad Dermatol 2002;46:394-8.)