[en] National Radiation Protection Institute in Prague organizes the TLD audit. The aim of the TLD postal audit is to provide control of the clinical dosimetry in the Czech Republic for purposes of state supervision in radiotherapy, to investigate and to reduce uncertainties involved in the measurements of absorbed dose and to improve consistency in dose determination in the regional radiotherapy centers. TLD audit covers absorbed dose measurements under reference conditions for ⁶⁰Co and ¹³⁷Cs beams, high-energy X-ray and electron beams of of linear accelerators and betatrons. The thermo-luminescence dosemeters are sent regularly to all radiotherapy centers. Absorbed dose measures by the TLD is compared to absorbed dose stated by radiotherapy center. Encapsulated LiF:Mg, Ti powder is used for the measurement. Deviation of 3% between stated and TLD measured dose is considered for photons and ±5% for electron beams. First TLD audit was started in 1997. A total of 135 beams was checked. There were found seven major deviations (more than ±6%), which were very carefully investigated. Medical Physicists from these departments reported a set-up mistake. However, at most of those hospitals with major deviations, an in situ audit in details was made soon after TLD audit. There were found discrepancies of clinical dosimetry but also bad technical state of some of the irradiation units. In 1998, second course TLD audit was started. No major deviation was found. Regular TLD audit seems to be a good way to eliminate big mistakes in the basic clinical dosimetry. Repeated audit in the regional radiotherapy centers that had major deviation during the first audit exhibited improvement of their dosimetry. It is intended to broaden the method and to control also beam parameters by means of a multi-purpose phantom. (authors)