We report the case of an 11-year-old boy suffering from a severe progressive chronic skin disease with clinical features of progressive systemic scleroderma, systemic lupus erythematosus and dermatomyositis. Skin biopsies revealed fibrosis and lichenoid changes and muscle biopsy a myositis. Immunohistology of the skin showed a lichen-ruber-like pattern. Despite repeated extensive investigations, no autoantibodies were detectable. Some of these findings looked like those described in juvenile dermatomyositis. Finally, it could be demonstrated that the boy showed microchimerism with approximately 1% maternal CD4+ lymphocytes in his peripheral blood leukocytes. Furthermore maternal cells could be demonstrated in inflamed muscle tissue. So a graft-versus-host-disease-like pathomechanism appears to be likely. Several systemic therapies have been used with limited success to improve the condition including corticosteroids, azathioprine, cyclosporine A and mycophenolate mofetil. A distinct improvement of erythemas and sclerosis could be achieved by means of low-dose UVA1 phototherapy which was applied with escalating single doses of 3-12 J/cm2 for 35 consecutive days.