[Clinical thinking and decision-making in the practice. A patient with thrombophlebitis].

A 55-year-old man presented with deep venous thrombosis of his left leg. Laboratory evaluation disclosed macrocytic anaemia and leukocytosis. In the clinical decision process it was not verified whether all symptoms fitted in with the presumptive diagnosis of pernicious anaemia and stomach carcinoma. The ultimate diagnosis was acute lymphocytic leukaemia. A proper evaluation of a peripheral blood smear would have led to this diagnosis earlier.