In this study, penitentiary disturbances are defined as 'a form of instrumental, collective protest which involves transgressions against laws or rules of the penitentiary and which is perceived to be 'beyond control' by the penitentiary authorities.' The analysis shows a great increase in the frequency of reported disturbances in Canadian prisons for 1971-80, with most of this increase occurring after 1976. These major findings are true for all medium- and maximum-security prisons treated as a group. An examination of disturbances by type of prisons treated as a group. An examination of disturbances by type of prison for each of the five regions indicates that the vast majority of reported disturbances occur in maximum-security prisons in all five regions. Relatively infrequent but fairly lengthy disturbances involving quite a few inmates were replaced during the 1977-80 period by disturbances that were more frequent but smaller (did not last as long nor involve as many inmates). The McGuigan inquiry (1977) offered an explanation for this pattern that emphasizes internecine conflict; i.e., disturbances are viewed as being caused by weak discipline and government in the prisons. McGuigan proposed that the prison director be reestablished as a strong figure in prison government. An 'addictive effect' hypothesis is suggested by study findings; Proposed recommendations for countering riots are critiqued. Twenty-three footnotes and 24 bibliographic entries are provided, along with graphic and tabular data.