Radiation doses that come from external as well as internal exposure pose a risk to nuclear industry workers. Internal exposure monitoring is known to be quite costly; therefore, it is important that resources are utilised with utmost effectiveness. In order to make this goal more feasible, guidelines for routine and special monitoring were designed. This was tested on various radionuclides that are the most problematic regarding internal dose assessment and that present the most concern. Some of these include tritium, cobalt-60, uranium, plutonium and thorium. A particularly important aspect of the methodology involved the assessment of uncertain intakes and doses of the monitoring measurements as well as how to reduce those uncertainties. Recommendations were offered on various monitoring methods, choice of measurement technique, monitoring intervals, measurement frequency, required measurement sensitivity and accuracy, required measurement parameters and uncertainty resulting in intakes and doses. Overall the improved reliability in assessing internal radiation doses will serve useful for managers and senior medical staff and nuclear industry regulators as well as commercial organisations providing dosimetry services.