Aim In addition to TNM stage, there are adverse tumour and host factors, such as venous invasion and the presence of an elevated systemic inflammatory response (SIR) that influence the outcome in colorectal cancer. The present study aimed to examine how these factors varied in screen detected (SD) and non-screen detected tumours (NSD). Method Prospectively maintained databases of the prevalence round of a biennial population FOBt screening programme and a regional cancer audit database were analysed. Interval cancers (INT) were defined as cancers identified within two years of a negative screening test. Results Of the 395 097 invited, 204 535 (52%) responded, 6159 (3%) tested positive, and 421 (9%) had cancer detected. From this cohort, a further 708 (63%) NSD patients were identified (468 (65%) non-responders, 182 (25%) INT cancers and 58 (10%) did not attend or did not have cancer diagnosed at colonoscopy). Comparing SD and NSD patients, SD patients were more likely to be male, and have a tumour with a lower Dukes stage (both p