A method is described for calibration of 192Ir high‐dose‐rate (HDR) brachytherapy afterloading systems. Since NIST does not offer calibration of ionization chambers with the gamma‐ray spectrum of iridium‐192, an interpolation procedure is employed, using calibrations above (137Cs, 662 keV) and below (250 kVcp, 146‐keV x rays) the exposure‐weighted average 192Ir energy of 397 keV. The same total wall+cap thickness must be used for both calibrations, and for the 192Ir measurements. A wall+cap thickness of 0.3 g/cm2 is recommended to assure charged particle equilibrium and to exclude secondary electrons emitted from the source encapsulation. Procedures are described for determining the corrections for source–chamber distance and room scatter during the source calibration in inverse‐square‐law geometry. A new well‐type ionization chamber has been designed specifically for convenient routine use with the HDR afterloading system. It can be calibrated by means of a previously calibrated 192Ir source, and offers a simple means for verifying the decay rate and for calibrating 192Ir replacement sources.