Background: Colonoscopic based surveillance is recommended for patients at increased risk of colorectal cancer. The appropriate interval between surveillance colonoscopies remains in debate, as is the "miss rate" for colorectal cancer within such screening programmes. Aims: The main aim of this study was to determine whether a one-off interval faecal occult blood test (FOBT) facilitates the detection of significant neoplasia within a colonoscopic based surveillance programme. Secondary aims were to determine if invitees were interested in participating in interval screening, and to determine whether interval lesions were missed or whether they developed rapidly since the previous colonoscopy. Patients: Patients enrolled in a colonoscopic based screening programme due to a personal history of colorectal neoplasia or a significant family history. Methods: Patients within the screening programme were invited to perform an immunochemical FOBT (Inform). A positive result was followed by colonoscopy; significant neoplasia was defined as colorectal cancer, adenomas either ≥10 mm or with a villous component, high grade dysplasia, or multiplicity (≥3 adenomas). Participation rates were determined for age, sex, and socioeconomic subgroups. Colonoscopy recall databases were examined to determine the interval between previous colonoscopy and FOBT offer, and correlations between lesion characteristics and interval time were determined. Results: A total of 785 of 1641 patients invited (47.8%) completed an Inform kit. A positive result was recorded for 57 (7.3%). Fifty two of the 57 test positive patients completed colonoscopy; 14(1.8% of those completing the FOBT) had a significant neoplastic lesion. These consisted of six colorectal cancers and eight significant adenomas. Conclusions: A one off immunochemical faecal occult blood test within a colonoscopy based surveillance programme had a participation rate of nearly 50% and appeared to detect additional pathology, especially in patients with a past history of colonic neoplasia.