Since Freud and other famous mental health scholars have put forth their postulations concerning the neurotic influences of religion in mental health, many of the 20th century mental health professionals have been influenced to hold skeptical and even hostile attitudes toward religion. However, the past two decades have increasingly found more empirical evidence supporting the beneficial effects of religiousness on mental health that apparently contrasts with the postulations of Freud. Evidence in research was nonetheless mainly based on physically healthy populations. Studies addressing the relationship between religiousness and mental health in physically vulnerable populations, such as the aged, ill and disabled, have been insufficient. For this reason, this paper reviews recent empirical studies published in peer-reviewed academic journals concerning these relatively neglected populations. Consequently, although the number of studies concerning these vulnerable populations is less than research on the general healthy populations, well-conducted studies did point out the beneficial effects of religiousness on physically vulnerable people. Apparently, religion is an important aspect of life in these populations during the times of suffering and stress. Finally, relevant theories explicating the relationship are reviewed and some theoretical implications are also addressed.