OBJECTIVE: No standard exists to measure religiosity in abortion studies. We test whether religiosity is associated with support for abortion among Mexican Catholics and whether different measures of degree of Catholicism alter the relationship. STUDY DESIGN: We conducted a nationally representative cross-sectional study using survey data from 2669 self-identified Mexican Catholics (response rate 85%). Our three outcomes were 1) overall support for legal abortion and support for abortion under exceptions, grouped as having 2) traditionally high agreement (rape, life) and 3) low agreement (on demand, socioeconomic). We used logistic regression controlling for sociodemographic covariates to test the association of four measures of Catholicism with our outcomes. RESULTS: The majority of Mexican Catholics support abortion in some circumstances. (90% at least one high agreement exception and 40% at least one low agreement exception). The only measure of degree of Catholicism significantly associated with all our outcomes was belief that a person who helps someone who aborts can be a good Catholic. Those who agreed (versus not) had higher odds of support for abortion for both high agreement (aOR 3.6 [95% CI: 1.7-7.9]) and low agreement (aOR 1.9 [95% CI: 1.3-2.7]) exceptions. Respondents who believe a woman who aborts does not need to confess (aOR 2.1 [95% CI: 1.5-2.8]) or needs to confess to God (aOR 1.4 [95% CI: 1.04-1.8]) versus a priest had higher odds of agreement with at least one low agreement exception. CONCLUSION: Opinion toward abortion among Mexican Catholics is diverse. More nuanced measures of Catholicism are valuable in assessing support for abortion, especially exceptions with low support. IMPLICATIONS: The main reasons women need abortion are precisely those with low support among Mexican Catholics. Focusing on nuanced measures of Catholicism can help us identify areas for shared values and frame messaging to meet the diversity of Catholic opinion. Catholicism is not an unsurmountable barrier to liberalization of abortion law.