In an evaluation of the Enhanced Thinking Skills (ETS; Cann et al., 2003) programme, reconviction at 1 year was higher for treatment non-completers (i.e. those allocated to treatment who started but did not complete) than for untreated prisoners (i.e. those not allocated to treatment). It may be that non-completion increases risk of reconviction for some offenders, hence efforts should be made to reduce non-completion rates. In designing retention strategies, the views of offenders are important. This study, conducted with adult male prisoners, elicited information from ETS non-completers (n = 18) about what interfered with programme completion. For comparison, views on ETS of completers (n = 6) were taken. The main themes were: (1) non-completers were motivated to stop offending and motivated for treatment; (2) compared with completers, non-completers saw ETS as less relevant and less well-timed in relation to their current concerns; (3) some non-completers found ETS too demanding, while others found ETS too slow and patronizing; and (4) working in a group was an area of dissatisfaction for non-completers. Limitations are the small sample size, varying reasons for non-completion, and gathering of offenders' views retrospectively. In future, treatment engagement should be studied prospectively, examining different categories of non-completers, and using larger samples. (PsycINFO Database Record (c) 2019 APA, all rights reserved)McMurran, M., McCulloch, A., & Babcock, B. B. B. C. C. C. D. D. E. F. F. H. K. M. M. M. P. R. R. S. W. Z. (2007). Why don't offenders complete treatment? Prisoners' reasons for non-completion of a cognitive skills programme. Psychology, Crime & Law, 13(4), 345-354. doi:http://dx.doi.org/10.1080/10683160601060424