Post-treatment surveillance of advanced ovarian cancer involves regular testing of asymptomatic patients using the CA125 test. This practice is based on a rationale that is not supported by evidence from clinical trials. This paper aims to stimulate critical reflection concerning the effect of investigative tests on clinical decisions and interactions, and the experience of illness, particularly in the context of advanced malignant disease. Drawing on the idea of the "medical gaze", and building on previous health communication research, we present an analysis of in-depth interviews and psychometric tests collected in a prospective study of 20 Australian women with advanced ovarian cancer conducted between 2006 and 2009. We describe the demands placed on patients by the use of the CA125 test, some hazards it creates for decision-making, and some of the test's subjective benefits. It is widely believed that the CA125 test generates anxiety among patients, and the proposed solution is to educate women more about the test. We found no evidence that anxiety was a problem requiring a response over and above existing services. We conclude that the current debate is simplistic and limited. Focussing on patient anxiety does not account for other important effects of post-treatment surveillance, and educating patients about the test is unlikely to mitigate anxiety because testing is part of a wider process by which patients become aware of a disease that -once it has relapsed -will certainly kill them in the near future.