Background Recently, symbols have been used to increase understanding of written information for people with intellectual disabilities, yet the effectiveness of this remains largely untested. This study was undertaken around the time of an election and it aimed to test whether a symbol-based manifesto increased the understanding of this material for people with intellectual disabilities. Method Two versions of a simplified manifesto were produced: one text-based and the other symbol-based (with text). Participants were randomly assigned to two groups: one received the text-based information, and the other the symbol-based information (with text). Participants were asked a series of questions about the material, both immediately (time 1) and a short time afterwards (time 2), to assess understanding (the material was in front of them throughout). Results Both versions produced relatively low levels of understanding. The group with symbols (and text) showed no better understanding than the group with text only. However, those with better language comprehension scores and those with better reading skills tended to show a higher understanding of the manifesto, in both groups. In the symbols group, those who said they had seen symbols before also showed significantly better understanding of the material at time 2. Conclusions This study suggests that the addition of symbols to simple texts does not necessarily improve people's understanding of it. It is proposed that a closer examination of people's understanding of symbols should be made and ways of improving this understanding investigated.