Religiousness has frequently been found to be associated with higher reported mental health levels than those found in individuals lower in reported religiousness. These results have often been inferred by scholars to mean that secular groups have poorer levels of mental health despite the fact that secular populations have rarely been included in studies. In this study, an ideologically diverse sample of 4,667 respondents was included to determine the relationships among general dogmatism levels, existential dogmatism, religiousness, and 5 indicators of mental health. The sample mainly comprised agnostic, atheist, Buddhist, Christian, Jewish, and spiritual nonreligious participants. Statistical analyses indicated that atheistic and theistic groups showed no significant differences on 4 of the 5 mental health indicators. Existential dogmatism and religiousness had similar positive relationships with mental health, but each had weak predictive strengths. The implications of the current study are that secular and religious adherents have similar levels of mental health, which is contrary to expectations based on the previous literature.