There are many different potential screening strategies for colorectal cancer (CRC) that vary both in the likely magnitude of their benefits on CRC mortality and their impact on health services. Many approaches to CRC screening are cost-effective, but there is substantial uncertainty about the optimal approach. Decision models using Markov or microsimulation modelling that compare the cost-effectiveness of different screening strategies are useful in this regard. We have reviewed recent decision models that compare the cost-effectiveness of one-off flexible sigmoidoscopy screening with immunochemical faecal occult blood (FIT) based screening. Models consistently show that any population-based screening is cost-effective compared with no screening, and that FIT-based screening is more effective than one-off sigmoidoscopy screening. The combination of one-off sigmoidoscopy with FIT is more effective in saving lives than either modality alone, but has the greatest impact on health service resources. The recent decision to proceed with biennial FIT-based screening is consistent with current evidence.