The approach to inborn errors of metabolism (IEM) is a challenge for any medical specialty. This is a rapidly developing area. As scientific information expands, the study of metabolic diseases strengthens, and increases the need and interest in confirming or discarding such errors, in order to offer patients prompt and appropriate therapeutic alternatives. To achieve this, it is necessary to use a rational and orderly clinical approach that takes into account the possibility of an IEM, as well as other diseases resembling them. Also to rationalize the use of more specialized, and complex diagnostic aids, that generally are less accessible to the patient. We report the case of a patient with a history of perinatal noxa, and neurological disorders, whose clinical course did not progress. The importance of a systematic diagnostic process, based mainly on the clinical picture, is emphasized.