Although the majority of Americans consider themselves to be Christian and affiliated with various Protestant denominations, a quarter of the American population identify themselves as Roman Catholics who are the largest single religious denomination in the country. Yet, surprisingly, fairly little research has been published in the professional psychology literature about working with this very large and diverse group. Psychologists have an ethical responsibility to be aware of and respectful to diversity including diversity based on religious background, affiliation, and perspectives. The purpose of this brief reflection is to offer 6 important principles to keep in mind for professional psychologists to consider when they work with Roman Catholic clients. These include attending to Catholic diversity and multiculturalism, attending to issues beyond sexual ethics and sexual victimization, being aware of theological diversity of beliefs and practices, and securing consultation with Catholic clerics. We must proactively keep ourselves abreast of these issues to best serve our clients and the public.