An international workshop, under the auspices of Group d'Etude des Lymphomes de l'Adulte (GELA) took place in Deauville, France, in April 3-4, 2009. The European experts with a published or personal experience on interim-PET in lymphoma were invited to the meeting. The aim of the workshop was twofold: (1) to reach a consensus on simple, reproducible criteria for interim-PET interpretation in Hodgkin lymphoma and diffuse large B-cell lymphoma (DLBCL), and (2) to launch two or more international validation studies, in an attempt to validate these rules. We concisely report here the minutes of the meeting and the conclusions/statements that have been reached.