The current tolerable daily intake (TDI) for zearalenone (ZEN) of 0.25 μg/kg body weight (bw) per day established by the EFSA Panel for Contaminants in the Food Chain (CONTAM Panel) in 2011 is based on oestrogenicity in pigs. No new studies were identified to change this TDI. The modified forms of ZEN identified are phase I and phase II metabolites. Phase I metabolites are mainly formed through reduction. Phase II metabolites are formed by conjugation of ZEN and its phase I metabolites with glucose or sulfate, and in animals glucuronic acid. The few data on the occurrence of modified forms of ZEN indicated that cereal-based foods are the main source, containing amounts varying from a few up to 100% of ZEN. Most of the phase I metabolites have oestrogenic activity and it is assumed that their combined action will be additive. The CONTAM Panel found it appropriate to set a group TDI of 0.25 μg/kg bw per day expressed as ZEN equivalents for ZEN and its modified forms (phase I and phase II metabolites). To account for differences in in vivo oestrogenic potency, each phase I metabolite was assigned a potency factor relative to ZEN to be applied to exposure estimates of the respective ZEN metabolites. It was assumed that conjugates (phase II metabolites) of ZEN and its phase I metabolites, which per se have no oestrogenic activity, will be cleaved releasing ZEN and its phase I metabolites. These conjugates were assigned the same relative potency factors as their aglycones. The overall uncertainty associated with the present assessment is considered as high. It would rather overestimate than underestimate any risk of modified ZEN. Several aspects of the uncertainty could be reduced provided more data are made available on oestrogenicity of modified ZEN, in particular α-zearalenol, in pigs.