Background The UK Strategy on Managing High Risk of Serious Harm Offenders with Severe Personality Disorder proposes an important role for offender managers in completing case formulations about such offenders. There is little evidence on whether this can be achieved. Aim Our primary aims were to devise, implement and evaluate training in case formulation for offender managers. A secondary aim was to assess whether the training led to changes in offender manager attitudes towards working with offenders with personality disorder. Method A 5‐day training programme was delivered to 20 offender managers, whose ability to carry out case formulation was assessed before and after the training using a 10‐point quality checklist. Attitudes towards personality disorder were also assessed before and after. Qualitative feedback on the training was used to provide further insight into the findings. Results Offender managers showed a significant improvement in their ability to carry out case formulation following training, with 7 of the 10 quality domains on the quality checklist rated as at least ‘satisfactory’ post training. Qualitative feedback highlighted reasons for some of the shortfalls in two of the three areas that did not show improvement. Improvements were shown in attitudes towards working with offenders with personality disorder in two of three domains. Conclusion Our findings provide further evidence for the effectiveness of training offender managers in case formulation. This is encouraging in terms of extending implementation of the Offender Personality Disorder Pathway, but a full trial is indicated, partly not only because sample sizes have been small so far, but also because the participants have been enthusiastic volunteers rather than randomly selected offender managers, and there are indications from other work that we know too little about optimal extent of training and about whether its effects are sustained. Copyright © 2016 John Wiley & Sons, Ltd.