Paliperidone, the 9-hydroxy metabolite of risperidone, was approved on 20 December, 2006 by the US Food and Drug Administration for the treatment of schizophrenia. It is also being tested for the treatment of bipolar mania. An on-line query of http://www.pubmed.gov and http://www.clinicaltrials.gov for 'paliperidone' and '9-hydroxy-risperidone' was done, along with an examination of poster presentations at scientific meetings held in 2006. Three 6-week pivotal clinical trials of paliperidone extended-release at fixed doses ranging from 3 to 15 mg administered orally once daily in the treatment of acute schizophrenia demonstrated superior efficacy to placebo. A favourable tolerability profile was also evidenced, except for prolactin elevation and dose-related extra-pyramidal effects. A relapse prevention study provides evidence of superiority of paliperidone over placebo in the maintenance of response. Safety has also been assessed in patients with schizophrenia who are 65 years or older. At present there are no studies available that are powered to directly compare paliperidone to other second-generation antipsychotics, including risperidone. With the impending availability of oral risperidone as a generic medication, cost of oral paliperidone will likely become a significant obstacle to its use.