OBJECTIVE: To investigate the quality of nuchal translucency measurements that were done as part of a randomised study into screening for Down's syndrome. DESIGN: Exploratory. METHOD: In the period May 2001-April 2003, 396 nuchal translucency measurements were done by 55 sonographers in 13 different echography centres. The sonographers were questioned in writing regarding their training and experience, the procedure and technique used, and the quality assurance. A filled-in questionnaire was received from 42 sono0 images at random from the 2710measurements (70%o) that had been made in 6 centres. These were evaluatedby 3 experts on the basis of the 5 criteria that are used by the Fetal Medicine Foundation (FMF). Each measurement was given 2 points for every criterion that was fulfilled, after which the average of the 3 scores was calculated. RESULTS: Of the 42 respondents, 88% had taken a nuchal translucency measurement course and 45% were certified by the FMF. Calipers were placed incorrectly by 50% of the respondents; 62% of the respondents mentioned the absence of an intern quality check. Concerning the quality-assessment of the nuchal translucency measurements, the assessors unanimously considered i3%o of the 30 images to be suitable for prenatal screen4ngand 43% to be unsuitable; their opinions as to the remaining images differed. The average quality mark was 4.7. CONCLUSION: Many nuchal translucency measurements did not fulfil the quality criteria that are imposed in order to make the measurement reliable as a screening test. There was a lack of quality securance in the echography centres