Understanding the reasons for the failure or the success of NPFM reforms is an issue that has recently attracted the attention of public sector management literature. Basing on the Italian Local Government -LG- case, the research analyses the NPFM reform actual implementation, and contributes to the theoretical debate about the reasons for the discrepancies between actual and formal accounting changes using an institutional approach. To this end a survey carried out on a statistically representative random sample of Italian municipalities with more than 5,000 inhabitants together with semi-structured interviews to privileged observers are used. According to the results of the analysis, the Italian NPFM reforms introduction can be regarded as a case wherein innovation heralded by the law is rather formal than substantial. As regards the reasons for the gap between formal and actual changes the study findings suggest the hypotheses of a direct correlation between accounting practices and respectively isomorphic pressures affecting the introduction of the new accounting tools -New institutional sociology (NIS)-, municipality’s organisational culture -Old institutional economics (OIE)- and municipalities’ size