Tetrodotoxin (TTX) and its analogues are a well-known toxin because of severe and lethal incidents in people consuming pufferfish (fugu) and occasionally other seafood . Several years ago it was detected in shellfish from European waters, first in Greece , then the UK  and subsequently the Netherlands . In Greece this was based on follow-up of false-positive test results in the mouse bioassay, in the two other countries after targeted LC-MS analysis of mussels and oysters. The producing organism of the toxin is still unclear, as well as the exact conditions leading to the formation and contamination of shellfish. It is also unclear whether this is a new phenomenon or has been undetected thus far, potentially due to no clear poisoning cases at the levels present in the shellfish or an extension of the harvesting period, now covering also the summer months.Surprisingly, no proper risk assessments, including health based guidance values, had been published for this well-known group of toxins, although in Japanese papers a Minimum Lethal Dose of 2 mg is mentioned. Other papers mention hospitalization of consumers after an estimated intake of 0.2 mg TTX. EFSA was therefore asked by the European Commission to perform a risk assessment . Based on a novel study in mice , EFSA derived an acute reference dose (ARfD) of 0.25 µg/kg bw. This was based on a NOAEL of 25 µg/kg bw and an uncertainty factor of 100. Reported human cases did not allow their use for deriving a reference point for the assessment but indicate that the ARfD is not conservative. EFSA also calculated that a large portion size of 400 gram shellfish should not contain more than 44 µg/kg of TTX or analogues to exclude effects in consumers. This level is occasionally exceeded, as shown in monitoring programs.