The purpose of this study is to elucidate the psychological impact of disclosure of genetic test results concerning hereditary non-polyposis colorectal cancer (HNPCC) and to assess factors associated with it, with particular focus on memory function. The subjects were persons who were suspected of having HNPCC and given the choice of undergoing genetic testing. The post-genetic testing psychological impact was evaluated by means of the Impact of Event Scale-Revised (IESR), and personality tendencies and memory function were evaluated. Final data were obtained from 46 subjects. The results of the genetic testing were ‘mutation-positive’ in 18 subjects, ‘uninformative’ in 18 subjects, and ‘mutation-negative’ in 10 subjects. Comparison of the IES-R scores showed that they tended to be higher in the mutation-positive group, but the differences were not statistically significant. The personality tendency ‘nervousness’ and verbal memory assessed prior to disclosure were significantly associated with total score on the IES-R. Based on the results of this study it seems possible to minimize the risk of a psychological impact of disclosure of genetic test results by reassessing the follow-up system for persons at high risk of a psychological impact.