Religious beliefs and practices are related to mental health. Many individuals report a religious affiliation, but do not have specific religious beliefs or practices such as attending religious services. These non-attendees are often assumed to resemble the non-religious, but are poorly studied. This study explored the demographic characteristics and mental health outcomes associated with being a non-attendee using data from a nationally representative Australian sample. Non-attendees were more likely to be non-Christian than attendees at religious services. They had worse mental health than both non-religious individuals and attendees, especially compared to the non-religious. Whether non-attendance is a result of or cause of poor mental health outcomes is not clear and deserves further investigation. Non-attendees clearly differed in our sample from both non-religious individuals and attendees. Our results do not support the hypothesis that individuals who report a religious affiliation, but are not actively religious, are similar to non-religious individuals.