A brain-computer interface (BCI) directly uses brain-activity signals to allow users to operate the environment without any muscular activation. Thanks to this feature, BCI systems can be employed not only as assistive devices, but also as neurorehabilitation tools in clinical settings. However, several critical issues need to be addressed before using BCI in neurorehabilitation, issues ranging from signal acquisition and selection of the proper BCI paradigm to the evaluation of the affective state, cognitive load and system acceptability of the users. Here we discuss these issues, illustrating how a rehabilitation program can benefit from BCI sessions, and summarize the results obtained so far in this field. Also provided are experimental data concerning two important topics related to BCI usability in rehabilitation: the possibility of using dry electrodes for EEG acquisition, and the monitoring of psychophysiological effects during BCI tasks.