Thymoma-associated multiorgan autoimmunity is a relatively new term to describe the rare paraneoplastic syndrome that complicates thymoma, which can involve the thyroid, liver and intestine in addition to the skin. The pathology often indicates a graft-versus-host-like pattern commonly observed in recipients of an allogeneic haematopoietic cell transplant. We report a case of type B2 and B3 thymoma with invasion to the lung and pleura in a patient who presented with oral lichen planus and graft-versus-host-like erythroderma. The cutaneous lesions improved after complete resection of the thymoma in combination with systemic glucocorticoids, which was subsequently complicated by cytomegalovirus pneumonitis.