Resumo. This work was developed with the purpose of studying the efficiency of the models which express the density-diameter relationship in stands of Pinus taeda L., implanted in several spacing and handled in unthinning density, and were measured every year until the of 18 age. Results indicated that all of the sizedensity relationship of Tang model presented good statistical precision, was more efficient than the others, presenting excellent coefficient of determination (0.99), low standard error of estimate (0.0948), low coefficient of variation (1.17%), low bias (0.0086) and high efficiency (0.8976). The slope of the sizedensity didn¿t allow proving the universality of the self-tinning law, with value of this slope is equal -3/2. With help of the size-density model, 6 Indexes of Density of the Stands (IDPs) were generated, with variation from the maximum 1400 to the minimum 600, with interval of class of IDP equal to 200, having as reference the standard diameter of 25 cm. The population¿s Density Management Diagram (DMD), elaborated for the dendrometric variables - average diameter, basal area and volume for hectare (by IDP) - presented good efficiency with low mistake in the estimate of the values of these variables. Real volume and estimate volume per hectare in DMD presented an absolute difference of just -7.39 m3ha-1 and a relative difference of -1.79 %, showing a great precision of the DMD model. The estimates volume of DMD per hectare, in relation to the real values, presented a value of efficiency equal to 0.99, what indicates a high precision, and an X 2 value equal to 0.00034, not significant to 0.01% of probability, demonstrating that the real and the estimate values don't differ statistical amongst themselves.