We have developed a reliable and valid questionnaire to measure the psychological consequences of screening mammography. The questionnaire measures the effect of screening on an individual's functioning on emotional, social, and physical life domains. Content validity was ensured by extensive review of the relevant literature, discussion with professionals and interviews with attenders at a pilot Breast X-ray Screening Program in Melbourne, Australia. Discriminant validity was assessed by having expert judges sort items into dimensions which they appeared to be measuring. Acceptable levels of concordance (above 80%) with a priori classifications were found. Concurrent validity was demonstrated by comparison of subscale scores of 53 attenders at the Breast X-ray Program with an independent interview assessment of dysfunction on each of the emotional, social and physical dimensions. There was over 79% agreement between interview scores and questionnaire scores for each dimension. Construct validity was confirmed by showing that subscale scores varied in predicted ways. For women who were recalled for further investigation, scores on each subscale measuring negative consequences, were higher at the recall clinic than at screening clinic (emotional: t = -7.28; df = 70; P less than 0.001; physical: t = -2.53; df = 70; P = 0.014; social: t = -2.49; df = 70; P = 0.015). The internal consistency of all subscales was found to be acceptable. This questionnaire is potentially useful for assessing the psychological consequences of the screening process and should have wide application.