The present study investigates the processing of presupposition accommodation. In particular, it concerns the processing costs and the time-course of accommodation as compared to presupposition satisfaction. Data collected in a self-paced word-by-word reading times experiment support three results. First, independently on the presupposition trigger in use, accommodation is costlier than satisfaction. Second, presupposition accommodation takes places immediately just as the trigger becomes available and proceeds incrementally during the sentence processing. Third, accommodated information is harder to be recalled. The results offer evidence for the on-line processing of presuppositions and, consistently with the traditional semantic framework, support the idea that, presuppositions are semantic properties encoded in the lexical meaning of the presupposition triggers.