Summary Subcorneal pustular dermatosis (SPD), or Sneddon–Wilkinson disease, is a rare pustular skin disease that follows a chronic relapsing course. A well‐known association exists between SPD and IgA monoclonal gammopathy of undetermined significance (MGUS), which exists in up to 40% of cases. SPD has also been observed in patients with IgA myeloma. In SPD, direct and indirect immunofluorescence studies do not reveal in vivo bound IgA to the epithelial cell surface, in contrast to IgA pemphigus, which has similar clinicopathological features. Here we describe the case of a male patient with SPD and a concurrent IgA MGUS who had been treated with dapsone for 20 years with frequent relapses. Following development of multiple myeloma, the patient was treated with intensive antimyeloma treatment consisting of high‐dose melphalan with autologous stem cell transplantation. This resulted in a complete remission of the myeloma with disappearance of the M‐protein. In addition, a sustained remission of SPD was achieved without further treatment. Twenty‐eight months after melphalan therapy the M‐protein reappeared in the serum, and 2 months later SPD reappeared with histopathologically proven skin lesions at predilection sites. Presence and absence of skin lesions was found to correlate with the presence and absence of the M‐protein in the serum. This is the first report of antimyeloma therapy inducing a long‐lasting remission in SPD. The findings in this patient strongly suggest a causal role for circulating IgA antibodies in the pathogenesis of SPD. Antimyeloma treatment should be considered in patients with IgA MGUS‐associated SPD refractory to other therapies. What's already known about this topic? Subcorneal pustular dermatosis (SPD) is highly associated with IgA monoclonal gammopathy of undetermined significance (MGUS) and IgA myeloma. The pathogenesis of SPD is poorly understood. What does this study add? The observed association between the presence and absence of SPD skin lesions and the presence and absence of IgA M‐protein in the serum suggests a causal role for circulating IgA antibodies in the pathogenesis of SPD. Antimyeloma treatment should be considered in patients with IgA MGUS‐associated SPD refractory to other therapies.