Summary This report describes the production of ERM®-AD624, a Listeria monocytogenes DNA material certified for the size of the DNA fragments obtained by enzymatic restriction digestion and Pulsed Field Gel Electrophoresis (PFGE). This material was produced following ISO Guide 34:2009 [ ] and is certified in accordance with ISO Guide 35:2006 [ ]. The CRM was produced from a culture of Listeria monocytogenes strain H2446 and processed into agarose plugs suitable for PFGE. The bacteria were lysed to release the DNA within the plugs. Between unit-homogeneity and stability during dispatch and storage were assessed in accordance with ISO Guide 35:2006. The material was characterised by an interlaboratory comparison of laboratories of demonstrated competence and adhering to ISO/IEC 17025. Technically invalid results were removed but no outliers were eliminated on statistical grounds only. Uncertainties of the certified values were calculated in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM). The material is intended for quality control and assessment of method performance. As with any reference material, it can be used for establishing control charts or validation studies. The CRM is available in plastic screw cap vials containing one plug suspended in TE solution. The minimum amount of sample to be used is the whole CRM.