This document provides criteria for quality assurance and quality control, evaluation of the performance, and the accreditation of biological dosimetry by cytogenetic service laboratories using the dicentric assay performed with manual scoring. This document addresses a) the confidentiality of personal information, for the requestor and the service laboratory, b) the laboratory safety requirements, c) the calibration sources and calibration dose ranges useful for establishing the reference dose-effect curves that contribute to the dose estimation from unstable chromosome aberration frequency and the detection limit, d) the scoring procedure for unstable chromosome aberrations used for biological dosimetry, e) the criteria for converting a measured aberration frequency into an estimate of absorbed dose, f) the reporting of results, g) the quality assurance and quality control, h) informative annexes containing sample instructions for requestor, sample questionnaire, sample report, fitting of the low dose-response curve by the method of maximum likelihood and calculating the error of the dose estimate, odds ratio method for cases of suspected exposure to a low dose, a sample calculation and sample data sheet for recording aberrations.