The Panel on Plant Health performed a pest categorisation of European isolates of Citrus tristeza virus (CTV) for the European Union (EU) territory. European CTV isolates are listed in Annexes IIAII and IIB of Directive 2000/29/EC. CTV is a well-defined and easily diagnosed Closterovirus species transmitted by the vegetative multiplication of infected hosts and through the activity of aphid vectors. Toxoptera citricida is the most efficient vector but Aphis gossypii is the most important in Europe. European isolates of CTV have been reported in seven of the eight EU Member States (MSs) with significant citrus production. The natural host range of CTV is restricted to citrus species and to a few, related genera, such as Fortunella and Poncirus. CTV is unlikely to be affected by ecoclimatic conditions in regions where its host plants are grown and has the potential to establish in southern regions of the EU territory. The majority of European CTV isolates cause severe decline symptoms (tristeza disease) in several citrus species, in particular sweet orange and mandarin grafted on susceptible sour orange or lemon rootstocks, which are commonly used in many EU MSs with the exception of Spain and, to a lesser extent, France. Symptoms of the severe stem pitting disease (SP) have not been reported by any EU MSs, despite the identification of isolates closely related to non-European isolates that cause SP in other regions of the world. The observed impact of CTV is on citrus industries still heavily reliant on susceptible rootstocks. Replacing those with CTV-tolerant rootstocks, as was done in Spain, virtually eliminates the impact of CTV in the absence of SP. Comprehensive certification systems can also reduce CTV spread and impact. The most critical area of uncertainty concerns the potential ability of some European isolates to cause SP in sweet orange.