Abstract: Deuterated forms of volinanserin according to structural formula (I), and their pharmaceutically acceptable salts, pharmaceutical compositions containing these compounds, and methods of treatment or prevention using these compounds or pharmaceutical compositions are described. The compounds are useful for treating or preventing a disease or condition selected from psychosis, schizophrenia, schizoaffective disorder, Parkinson's disease, Lewy body dementia, sleep disorder (including insomnia), agitation, mood disorder (including depression), thromboembolic disorder, autism, and attention deficit hyperactivity disorder.