[Clinical reasoning and decision making in the practice. A woman with abdominal complaints].

A female patient aged 28 years suffered from recurrent episodes of diarrhoea. Giardia lamblia was isolated once. By rigorous application of basic clinical skills, such as thorough history taking and physical examination, together with laboratory tests the correct diagnosis was established (in this patient systemic lupus erythematosus). Two important aspects of clinical reasoning, viz. returning to the patient when new information becomes available (cyclic way of working) and pattern recognition ensured a fruitful diagnostic process.