Publishing data about individuals without revealing sensitive information about them is an important problem. Distributed data mining applications, such as those dealing with health care, finance, counter-terrorism and homeland defence, use sensitive data from distributed databases held by different parties. This comes into direct conflict with an individual’s need and right to privacy. It is thus of great importance to develop adequate security techniques for protecting privacy of individual values used for data mining. Here, the authors study how to maintain privacy in distributed mining of frequent item sets.