A 26-year-old woman with Crohn disease was seen with a widespread pustular eruption, most prominent on the hands and feet, after treatment with certolizumab pegol was initiated 4 months earlier. Psoriasiform plaques were widespread over the trunk, extremities (Figure 1), and scalp, and she also had substantial palmoplantar involvement. Over her lateral malleoli were pink-red scaly plaques rimmed with pustules (Figure 2). She denied personal or family history of psoriasis. Two punch biopsy specimens from the left lateral malleolus revealed focal mild spongiosis, parakeratosis, slight acanthosis, a predominantly lymphocytic inflammatory dermal infiltrate, and exocytosis of neutrophils.