This study explores the impact of participation in a series of moral case deliberations (MCD) on the moral craftsmanship (MCS) of Dutch prison staff. Between 2017–2020, ten MCDs per team were implemented in three prisons (i.e., intervention group). In three other prisons (i.e., control group) no MCDs were implemented. We compared the intervention and control group using a self-developed questionnaire, administered before (pre-measurement) and after the series of MCDs (post-measurement). Results After the MCDs, participants scored significantly higher on 7 of (...) the 70 items related to MCS. On some items there were significant impact differences between the various professional disciplines. Discussion Possible explanations for a relatively low impact are discussed. A shorter and validated questionnaire is needed in order to further study the MCS of professionals and the impact of Ethics Support Services (ESS). Conclusions There was a positive development on some elements of MCS after participation in a series of MCDs. (shrink)