Techniques are disclosed for aggregation in uncertain data in data processing systems. For example, a method of aggregation in an application that involves an uncertain data set includes the following steps. The uncertain data set along with uncertainty information is obtained. One or more clusters of data points are constructed from the data set. Aggregate statistics of the one or more clusters and uncertainty information are stored. The data set may be data from a data stream. It is realized that the use of even modest uncertainty information during an application such as a data mining process is sufficient to greatly improve the quality of the underlying results.