To examine the 'cancer effect' (higher risk perceptions and negative emotion in cancer-related contexts) on young women's responses to overdiagnosis (identification and treatment of inconsequential disease) in cervical cancer screening.,In a randomised experimental study, 168 women aged 17-24 read 1 of 4 texts outlining benefits and harms of cervical cancer screening or a fictitious non-cancer screening test; each presented with or without overdiagnosis information. Screening intentions and psychosocial outcomes were measured (T1). Overdiagnosis information was then presented to participants who did not receive it initially and intentions reassessed (T2).,Mean screening intentions were not significantly different across groups. The distribution of intentions for cancer vs non-cancer screening differed significantly. Cancer information led to more extreme responses. Participants receiving overdiagnosis information at T2 reduced their screening intentions significantly. Perceived risk of disease was lower when overdiagnosis information was presented (non-cancer condition only). Higher negative emotion predicted higher screening intentions (cancer condition only).,This pattern of results suggests that a 'cancer effect' may be present among young women given identical information about cancer and non-cancer screening.,The 'cancer effect' may contribute to community eagerness for cancer screening despite provision of information about harms like overdiagnosis.