The SWI/SNF complex contributes to the regulation of gene expression by altering the chromatin structure. Depending on the context, it can be involved in either transcriptional activation or repression. Growing genetic and molecular evidence indicate that subunits of the SWI/SNF complex act as tumor suppressors in human and mice. Results from biochemical and transfection studies suggest also that SWI/SNF participates either in the inhibition or activation of several oncogenes and tumor suppressor genes and/or control their transcriptional activity. These activities provide molecular insight into the mechanism underlying SWI/SNF function in tumor suppression.