A woman in her 50s presented with a diffuse, symmetrically distributed rash that first began at age 10 years as migratory erythematous plaques that gradually spread centrifugally, forming large figurate lesions that later became fixed. Physical examination revealed well-defined, polycyclic, and geographic hyperkeratotic plaques that involved the axillae, chest, flanks, inguinal folds, and buttocks (Figure). The remainder of the physical examination and routine laboratory study results were unremarkable. Her family history was notable for a relative with similar, undiagnosed lesions. Prior treatment had included multiple topical corticosteroids and antifungal agents without improvement. Histopathological examination disclosed irregular acanthosis with compact hyperkeratosis/orthokeratosis and a mild perivascular lymphocytic infiltrate in the superficial dermis. Fungal stain results were negative for hyphae. Clinicopathologic features were consistent with the diagnosis of erythrokeratodermia. Genetic testing was not performed due to the cost. She was treated with isotretinoin (0.3 mg/kg/d), with partial improvement.