[en] The evaluation of the radiological impacts associated with uranium mining activities requires a comparison, for each environmental compartment, of data taken before and after the end of mining works. In the case of the Portuguese old uranium mines, with a few exceptions environmental data about the natural background collected before the beginning of the exploitation is scarce; thus, only the actual situation can be well characterized. A possible way to overtake this limitation is to obtain data from areas which constitute a natural analog of those that were mined for uranium ores, but where exploitation did not occur. In order to fill the necessary requirements, a reference area should be located in the same metallogenetic province, and have similar geological, geo-morphologic, hydrogeological and climate conditions relatively to those prevailing in the mined areas; moreover, land use should be also similar. The Oliveira do Hospital area, located in Central Portugal, fulfill such requirements. Here late-tectonic Hercynian granites and pre-ordovician meta sedimentary rocks dominate. Uranium ores occur in faults (vein-type) or are disseminated in the metasediments, which is the typical geological setting observed in most portuguese uranium mines. Data from detailed gamma -ray surveys carried out in the area show the existence of a high variability of the natural background, with values ranging between 200 and 15000 cps (counts per second) on a Saphymo S.P.P.2 equipment. The external radiation follows the same trend ranging from 0.16 to 2.12 micro Gy.h-1. The determination of radionuclides was performed in 14 samples of soils, 5 of river sediments, 24 of surface water and groundwater and also in 5 plants used as foodstuff by the local population. The concentration of long-lived radionuclides in dust was also evaluated, as well as indoor and outdoor radon. The activity of the radionuclides also shows, in a general way, high variability. For example, ²³⁸U varies between 169 and 650 Bq.kg^-1 in soils, and between 154 e 391 Bq.kg^-1 in sediments; ²²⁶Ra has values between 137 e 986 Bq.kg^-1 (soils) and between 116 and 377 Bq.kg^-1 (sediments). For water samples the activity of 226 Ra ranges in a large interval from 0.01 to 1.76 Bq.l^-1. The variation in the activity of ²²⁶Ra in plants is also high, with the lowest value observed in potatoes (0.23 Bq.kg^-1) and the highest in cabbage (18.9 Bq.kg^-1). The activity of long-lived radionuclides in dust is lower than the detection limit, indoor radon averages 279 Bq.m^-3 and outdoor radon averages 650 nano J.m^-3. The results obtained and the assumption of a realistic scenario for different groups of population allowed to evaluate the dose for the exposition to ionizing radiation from natural sources. Thus, an effective dose of 6.8 mSv.y-1 was estimated for the urban population while for the rural population the estimated average is of 5.9 mSv.year^-1. These values are higher than the average ascribed for the general population in Portugal (4.7 mSv.year^-1) and should be taken into account for clean-up goals in the process of environmental remediation of the old uranium mines. (authors)