Recently, at the Karlsruhe Research Centre, a computer-based expert system, Internal Dose Equivalent Assessment System (IDEA System), has been developed for assisting dosimetrists in applying the relevant recommendations and guidelines for internal dosimetry. The expert system gives guidance to the user with respect to: (a) planning of monitoring, (b) performing routine and special monitoring, and (c) evaluation of primary monitoring results. The evaluation is done according to the IDEA System guidelines (Doerfel, H. et al., General guidelines for the estimation of committed effective dose from incorporation monitoring data. Research Report FZKA 7243, Research Center Karlsruhe, Karlsruhe (2006). ISSN 0947-8260.) in a three-stage procedure according to the expected level of exposure. At the first level the evaluation is performed with default or site-specific parameter values, at the second level case-specific parameter values are applied and at the third level a special evaluation is performed with individual adjustment of model parameter values. With these well-defined procedures the expert system follows the aim, in which all recommendations and guidelines are applied properly and the results in terms of committed effective and organ doses are close to the best estimate.