Introduction An Interdisciplinary Expert Committee was created by four Spanish Scientific Societies, organisers of external quality assurance programs, to provide laboratories a consensus of minimum analytical quality specifications with the aim of assuring similar analytical performance all over Spain. Material and method A total of 1,262,623 results was obtained from 3688 laboratories and 24 periods studied (2005 and 2006). For each analyte, the absolute difference between the result and the comparative value (peer group mean), expressed in percentage, was calculated and named “error”. From the error frequency distribution, the 95 percentile was considered as “candidate specification”. This value was compared with the specification used in Germany and USA and, in the case of being higher than one of them, the “candidate specification” value was increased iteratively, until 90% of participating laboratories had 75% of their results within the “candidate specification”. This value was considered to be the specification and the process ended. Results and conclusion Specifications for 37 analytes (3 immunology, 5 therapeutic drug monitoring, 15 hormones and tumour markers, 14 haematology and coagulation are proposed. They are considered to be the minimum level of quality that each laboratory had to reach, to assure common analytical performance. If the results in the external quality assurance program exceed these specifications, an immediate review should be made and, if necessary, corrective actions should be taken.