Deficiencies in the delivery of community mental health services in developed countries have been adduced as the reason for the large number of mentally ill in prisons. The large number of mentally ill persons found in prisons in many countries that have different mental health systems, however, could be an indication that system delivery may not be the only reason for this phenomenon. It may be that the “balloon theory” whereby it has been sustained that as mental hospitals beds decrease, prison beds increase and vice-versa will have to be reconsidered. In this presentation, data indicating the flow of mental patients into prisons in several countries will be reviewed. This type of data, however, tends to be statistical aggregates that will need to be contrasted with theoretical considerations and case reviews of mentally ill inmates in order to demonstrate that a relationship between mental illness and crime does exist at different levels of interaction. Such a relationship may be a more fundamental reason for mentally ill persons ending up in prisons than systemic service delivery concerns.