Our objective was to test a theoretical model that explains quality of life as a function of the intrusiveness of illness encroaching on the different domains of one's life. The intrusiveness of illness is explained not only by disease and treatment related factors, but also by one's psychological and social resources (Devins, 1994). To investigate this issue, a sample of 336 women aged 50 and under, recently diagnosed with breast cancer were interviewed in their homes. Consistent with Devins' model, intrusiveness of illness mediated the effect of disease and treatment factors on quality of life. Contrary to his model, some treatment factors also had direct effects while social and psychological factors had only direct effects on quality of life. Neither time post-diagnosis nor type of treatment affected the psychological component of quality of life. © 1998 John Wiley & Sons, Ltd.