BACKGROUND Proximal nail fold inflammation can be caused by many diseases and has not previously been recognized as a result of posterior embedding of the nail. We describe a new pattern of ingrowth that we have termed retronychia ("retro"--Latin for backwards; "onychia"--Greek for nail). The term describes a combination of proximal nail plate ingrowth into the proximal nail fold which is associated with multiple generations of nail plate misaligned beneath the proximal nail. OBJECTIVE To describe a new pattern of nail ingrowth which causes a specific form of proximal nail fold paronychia. METHODS Collective cases were reported to a European Nail Society expert group. RESULTS Persistent proximal nail fold inflammation can result from an episode of trauma that disturbs longitudinal nail growth and results in reverse embedding of the nail plate. This can cause pain, inflammation, and granulation tissue formation, and is typically relieved by avulsion and antiinflammatory treatment. CONCLUSIONS We cannot demonstrate causality between the proposed precipitants and the clinical features. CONCLUSIONS Retroncyhia represents proximal ingrowth of the nail that occurs when the nail embeds backwards into the proximal nail fold. Nail plate avulsion with supplementary medical management is curative.