It is observed an increasing interest on the estimation of measurement uncertainty to deciding on conformity and quality assurance, mainly in the fields of environment, safety, health and industry, in which the measurement results are critical once they directly deal with human beings. According to studies performed in Australia, England, Turkey and Brazil, a great concern is observed with the reliability of the results obtained for blood pressure measurements by noninvasive mechanical sphygmomanometers. In these studies, errors of up to 4,4 kPa (33 mmHg) were obtained in the evaluated instruments, against the value of maximum error of 0,53 kPa (4 mmHg) required by OIML R 16-1:2002. Nowadays, the evaluation of the reliability of these measurement instruments for medical diagnosis is obtained considering only the measurement error (according to OIML R 16-1:2002), without taking into account the measurement uncertainty. Motivated to contribute for the metrological reliability of non- invasive mechanical sphygmomanometers, globally used in hospitals and residences, the present work aims at developing a model to associate the measurement uncertainty on the metrological reliability evaluation of these instruments. In order to perform the measurements with the sphygmomanometers, a set-up were prepared with environmental monitoring according to international recommendation (OIML R-16:2002) and national standards (ABNT NBR-14105:1998 and NIE-DMEL-006). The data of the present work were obtained by means of direct measurements in new and in use sphygmomanometers, utilizing a pressure pattern. Calculation of the following parameters was performed: measurement error, hysteresis, fiducial error and measurement uncertainty. The obtained results show that, as a function of the measurement uncertainty, the maximum permissible error of 0.53 kPa (4 mmHg) can be overcome. Considering the manometer measurement error, according to OIML R 16-1:2002, 60 % of the non- invasive mechanical sphygmomanometers evaluated were approved. When considering not only the measurement error, but also measurement uncertainty of the manometer, only 12% of the non-invasive mechanical sphygmomanometers were approved. Based on the present results, a reduction of the maximum permissible error for these instruments, incorporating the measurement uncertainty, without the need to calculate it in the verification procedure, is proposed. This work recommends not only a review of OIML maximum permissible error for sphygmomanometers, but also proposes a new configuration of the instrument, with reduction of intrinsic error and improvement of resolution.