A 45-year old man was admitted to an intensive care unit with flank pain and thrombocytopenia. He was treated for a suspected septicaemia but turned out to have signs of an unknown collagenosis which responded to plasma exchange, thymectomi and corticosteroids. Kidney biopsy revealed an intense tubulointerstitial reaction with suspected microthrombotic lesions in the vessels. The condition reoccurred with thrombocytopenia a couple of months later but responded to plasma exchange, corticosteroids and mycophenolate mofetil. An unknown collagenosis with findings of autoimmune thymitis and tubulointerstitial nephritis is the most probable cause of the condition.