A datum transformation between two geodetic datums primarily requires to compute transformation (datum) parameters through the common points whose the coordinates are available in both datums. The coordinates are burdened with errors caused by different reasons. During the estimation, some parts of these errors are absorbed into the parameters. Therefore, different combinations of common points lead to different sets of the datum parameters. Amounts of the differences between the different parameter sets are dependent on the amounts of the errors which are absorbed in the estimation. In this study, it is investigated how the distribution of common points effects on the estimations in datum transformation. The results of the investigations using two local applications in Turkey show that the point distribution highly determining factor on how much the errors effect on the estimations. (c) 2005 Elsevier Inc. All rights reserved.